Catalytic hydrogen storage electrode materials for use in electrochemical cells and electrochemical cells incorporating the materials

ABSTRACT

Disclosed is a reversible, electrochemical cell having a high electrochemical activity, hydrogen storage negative electrode. The negative electrode is formed of a reversible, multicomponent, multiphase, electrochemical hydrogen storage alloy. The hydrogen storage alloy is capable of electrochemically charging and discharging hydrogen in alkaline aqueous media. In one preferred exemplification the hydrogen storage alloy is a member of the family of hydrogen storage alloys, derived from the V-Ti-Zr-Ni and V-Ti-Zr-Ni-Cr alloys in which the V, Ti, Zr, Ni and Cr are partially replaced by one or more modifiers, and the alloy has the composition: 
     
         (V.sub.y&#39;-y Ni.sub.y Ti.sub.x&#39;-x Zr.sub.x Cr.sub.z).sub.a M&#39;.sub.b M&#34;.sub.c 
    
      M d   iv   
     where x&#39; is between 1.8 and 2.2, x is between 0 and 1.5, y&#39; is between 3.6 and 4.4, y is between 0.6 and 3.5, z is between 0.00 and 1.44, a designates that the V-Ni-Ti-Zr-Cr component as a group is from 70 to 100 atomic percent of the alloy, b,c,d,e, . . . , are the coefficients on the modifiers, and M&#39;, M&#34;, M iii , and M iv  are modifiers which may be individually or collectively up to 30 atomic percent of the total alloy. The modifiers, M&#39;, M&#34;, M iii , and M iv  are chosen from Al, Mn, Mo, Cu, W, Fe, Co, and combinations thereof.

FIELD OF THE INVENTION

The present invention relates to rechargeable electrochemical cells.More particularly, the invention relates to rechargeable cells andbatteries having negative electrodes formed of multicomponent,multiphase, electrochemical hydrogen storage alloys. The negativeelectrodes are characterized by superior electrochemical properties,i.e., high cycle life, high capacity, high drain rates, high midpointvoltages, low self-discharge, and enhanced low temperaturebehaviorssures.

BACKGROUND OF THE INVENTION A. Principles of Operation

Secondary cells using rechargeable hydrogen storage negative electrodesare an environmentally non-threatening, high energy densityelectrochemical power source. These cells operate in a different mannerthan lead acid, nickel-cadmium or other battery systems. Therechargeable hydrogen storage electrochemical cell or battery utilizes anegative electrode that is capable of reversibly electrochemicallystoring hydrogen. These cells usually employ a positive electrode ofnickel hydroxide material, although other positive materials may beused. The negative and positive electrodes are spaced apart in analkaline electrolyte, which may include a suitable separator, i.e., amembrane, therebetween.

Upon application of an electrical potential across the cell, thenegative electrode material (M) is charged by the electrochemicalabsorption of hydrogen and the electrochemical evolution of hydroxylion:

    M+H.sub.2 O+e.sup.- →M-H+OH.sup.- (Charging)

Upon discharge, the stored hydrogen is released to form a water moleculeand evolve an electron:

    M-H+OH.sup.- →M+H.sub.2 O+e.sup.- (Discharging)

In the reversible (secondary) cells of the invention, the reactions arereversible.

The reactions that take place at the positive electrode of a secondarycell are also reversible. For example, the reactions at a conventionalnickel hydroxide positive electrode as utilized in a hydrogenrechargeable secondary cell are:

    Ni(OH).sub.2 +OH.sup.- →NiOOH+H.sub.2 O+e.sup.31 (Charging),

    NiOOH+H.sub.2 O+e.sup.-→Ni(OH).sub.2 +OH.sup.- (Discharging).

A secondary cell utilizing an electrochemically rechargeable hydrogenstorage negative electrode offers important advantages over conventionalsecondary cells and batteries, e.g., nickel-cadmium cells, lead-acidcells, and lithium cells. First, the hydrogen storage secondary cellscontain neither cadmium nor lead nor lithium; as such they do notpresent a consumer safety or environmental hazard. Second,electrochemical cells with hydrogen storage negative electrodes offersignificantly higher specific charge capacities than do cells with leador cadmium negative electrodes. As a result, a higher energy density ispossible with hydrogen storage cells than with conventional systems,making hydrogen storage cells particularly suitable for many commercialapplications.

B. BACKGROUND OF THE INVENTION: AB₂ TYPE HYDROGEN STORAGE ALLOYS

The hydrogen storage art provides a rich storehouse of hydrogen storagealloys, both electrochemical and thermal. One type of these alloys areexemplified by the AB₂ type hydrogen storage alloys. The prior artreferences teach basic C₁₄ and C₁₅ type Laves phase AB₂ materials with(1) one or more of Ti, Zr, and Hf, and (2) Ni, generally with one ormore additional metals. However, there is no teaching in any of theprior art references of either the local metallurgical, chemical, orelectrochemical relationships between the various individual metals thatpartially substitute for Ni, or that partially substitute for the Ti,Zr, and/or Hf. Nor is there any teaching of local, i.e., intra-phase,compositions and the effect of local, i.e., intra-phase, compositionaldifferences on catalytic properties, generally, and key determinants ofcatalytic properties, such as the electron work function.

The earliest teachings of AB₂ type hydrogen storage materials arethermal hydrogen storage alloys. In thermal hydrogen storage alloys thedriving forces for hydriding and dehydriding are thermal and pressuredriving forces. By way of contrast, electrochemical hydrogen storagealloys are hydrided and dehydrided by electron transfer processes inionic media.

Early reported members of the AB₂ class were the binaries ZrCr₂, ZrV₂,and ZrMo₂. These were reported to be thermal hydrogen storage alloys byA. Pebler and E. A. Gulbransen, Transactions of the MetallurgicalSociety, 239, 1593-1600 (1967).

Another early member of this class is the Mg-Ni thermal hydrogen storagealloy described by J. J. Reilly and R. R. Wiswall, "The Reaction ofHydrogen With Alloys of Magnesium and Nickel and the Formation of Mg₂NiH₄ " Inorganic Chem. (1968) 7, 2254. These early alloys of Reilly andWiswell were thermal hydrogen storage alloys, which hydrided anddehydrided by pressure and temperature driven processes, and not byelectron transfer with an external circuit.

F. H. M. Spit, J. W. Drivjer, and S. Radelar describe a class of ZrNibinary thermal hydrogen storage alloys in "Hydrogen Sorption By TheMetallic Glass Ni₆₄ Zr₃₆ And By Related Crystalline Compounds," ScriptaMetallurgica, 14, (1980) 1071-1076. In this paper Spit et al describethe thermodynamics of gas phase hydrogen adsorption and desorption inthe ZrNi₂ binary system.

Subsequently, in F. H. M. Spit, J. W. Drivjer, and S. Radelar, "HydrogenSorption in Amorphous Ni(Zr,Ti) Alloys", Zeitschrift Fur PhysikaischChemie Neue Folge Bd., 225-232 (1979) reported the gas phase hydrogensorption and desorption kinetics of thermal hydrogen storage processesin Zr₃₆.3 Ni₆₃.7 and Ti₂₉ Zr₉ Ni₆₂.

Zirconium-manganese binary thermal hydrogen storage alloys weredisclosed, for example, in F. Pourarian, H. Fujii, W. E. Wallace, V. K.Shina, and H. Kevin Smith, "Stability and Magnetism of Hydrides ofNonstoichiometric ZrMn₂ ", J. Phys. Chem., 85, 3105-3111. Pourarian etal describe a class of nonstoichiometric hydrides of the general formulaZrMn_(2+x) where x=0.6, 0.8, and 1.8. (ZrTi)-manganese ternary hydrogenstorage alloys were described by H. Fujii, F. Pourarian, V. K. Sinha,and W. E. Wallace, "Magnetic, Crystallographic, and Hydrogen StorageCharacteristics of Zr_(1-x) Ti_(x) Mn₂ Hydrides", J. Phys. Chem , 85,3112.

Manganese-nickel binary thermal hydrogen storage alloys were describedfor thermal hydrogen storage in automotive applications by H. Buchner in"Perspectives For Metal Hydride Technology", Prog. Energy Combust. Sci.,6, 331-346.

Ternary zirconium, nickel, magnanese thermal hydrogen storage alloys aredescribed in, for example, A. Suzuki and N. Nishimiya, "ThermodynamicProperties of Zr(Ni_(x) Mn_(1-x))₂ --H₂ Systems," Mat. Res. Bull., 19,1559-1571 (1984). Suzuki et al describe the system Zr(Ni_(x) Mn_(1-x))₂where x=0.2, 0.5, and 0.8.

Six component thermal hydrogen storage alloys of the general AB₂ typeare described in German Patentschrift DE 31-51-712-Cl for Titanium BasedHydrogen Storage Alloy With Iron And/or Aluminum Replacing Vanadium andOptionally Nickel, based upon German Application DE 31-51-712 filed Dec.29, 1981, of Otto Bernauer and Klaus Ziegler, and assigned to DaimlerBenz AG. The key teaching of Bernauer et al is that the vanadium in asix component Tl-Zr-Mn-Cr-V-Ni alloy can be partially replaced by Feand/or Al to give a lower cost thermal hydrogen storage alloy. Asecondary teaching is that the Ni can be partially replaced by Fe tofurther reduce the cost of the alloy. The key teaching is that Fe can beused in the alloy without hurting the properties.

Bernauer et al describe a thermal hydrogen storage alloy having thecomposition Ti_(1-a) Zr_(a) Mn_(2-x) Cr_(x-y) (VzNi_(1-z))_(y), where ais from 0 to 0.33, x is from 0.2 to 1.0, y is between 0.2 and x, and zis from 0.3 to 0.9. Bernauer et al disclose that the Ni is partiallyreplaceable by Co and/or Cu, and from 1 to 5 atomic percent of the Ti isreplaceable by strong oxygen getters, such as lanthanum and other rareearths. It is further disclosed that up to 20 atomic percent of thevanadium is replaceable by Fe, and up to 15 atomic percent of thevanadium is replaceable by Al, with the provision that no more than 30atomic percent of the V can be replaced by Fe and Al. It is furtherdisclosed that Ni atoms can be replaced by Fe atoms.

A further related teaching relating to multi-component thermal hydrogenstorage alloys of this general type is in German Patentschrift DE30-23-770-C2 for Titanium Manganese Vanadium Based Laves Phase MaterialWith Hexagonal Structure, Used As Hydrogen Storage Material, based uponGerman Application DE 30-23-770 filed June 25, 1980, and 30-31-471 filedAug. 21, 1980 of Otto Bernauer and Klaus Ziegler, and assigned toDaimler Benz AG. The key teaching of Bernauer et al is that the nickelin a six component Tl-Zr-Mn-Cr-V-Ni alloy can be partially replaced byCo and/or Cu to give a lower cost thermal hydrogen storage alloy.

The alloys disclosed in DE 30-23-770 are Ti_(1-a) Zr_(a) Mn_(2-x)Cr_(x-y) (V_(z) M_(1-z))_(y) in which M is one or more of Ni, Co, andCu, a is from 0.0 to 0.3, x is from 0.2 to 1.0, y is between 0,2 and thevalue of x, and the ratio of vanadium to total Ni, Co, and Cu is between9:1 and 3:2.

Matsushita Electric Industrial Co.'s U.S. Pat. Nos. 4,153,484 and4,228,145, to Gamo, Moriwaki, Yamashita, and Fukuda, both entitledHydrogen Storage Material, disclose a class of C14 type Laves phasematerials for the thermal storage of hydrogen. That is, the materialsare hydrided by gaseous hydrogen and dehydrided by evolving gaseoushydrogen. The disclosed C₁₄ materials have a hexagonal crystal structurewith an a lattice dimension of 4.80 to 5.10 Angstroms and a c latticedimension of 7.88 t 8.28 Angstroms. Gamo et al.'s disclosed thermalhydrogen storage alloys contain Ti-Zr-Mn, optionally with one or more ofMo, or Cu. This family of thermal hydrogen storage patents requires thepresence of Mn, is silent as to V, Cr, or Ni, and contains no teachingof additional materials.

Other Laves phase materials are disclosed in Matsushita's U.S. Pat. No.4,160,014 of Takaharu Gamo, Yoshio Moriwaki, Toshio Yamashita, andMasataro Fukuda for Hydrogen Storage Material, claiming the benefit ofJapanese Patent Application 52JP-054140 filed May 10, 1977. Gamo et aldisclose an AB_(a) type thermal hydrogen storage material where A is atleast 50 atomic percent Ti, balance one or more of Zr or Hf, B is atleast 30 atomic percent Mn, balance one or more of Cr, V, Nb, Ta, Mo,Fe, Co, Ni, Cu, and rare earths, and a is from 1.0 to 3.0.

Another class of thermal hydrogen storage materials is disclosed in U.S.Pat. No. 4,163,666 of D. Shaltiel, D. Davidov, and I. Jacob for HydrogenCharged Alloys of Zr(A_(1-x) B_(x))₂ And Method of Hydrogen Storage.Shaltiel et al. disclose the ternary Zr(A_(1-x) B_(x))₂ where A is ormore of V, Mn, or Cr, and B is one or more of Fe or Co. The material isdisclosed as a thermal hydrogen storage alloy.

Other prior art Laves phase-type hydrogen storage alloys are shown, forexample, in Matsushita Electric Industrial Co. Ltd. U.S. Pat. No.4,195,989 of Takaharu Gamo, Yoshio Moriwaki, Toshio Yamashita, andMasataro Fukuda for Hydrogen Storage Material, claiming the benefit ofJapanese Patent Applications 53JP-044677 filed Apr. 14, 1978, and52JP-130049 filed Oct. 28, 1977. Gamo et al disclose a Laves phasehexagonal Ti-Mn-M alloy where M is one or more of V, Cr, Fe, Co, Ni, Cu,and Mo, with the a parameter being between 4.86 and 4.90 Angstroms, andthe c parameter being between 7.95 and 8.02 Angstroms. These materialsare disclosed to be thermal hydrogen storage materials.

U.S. Pat. No. 4,397,834 of M. Mendelsohn and D. Gruen for "Method ofGettering Hydrogen Under Conditions of Low Pressure" describes a ternaryZr-V-Cr hydrogen storage alloy. The alloy, having the formularepresented by Zr(V_(1-x) Cr_(x))₂, where x is from 0.01 to 0.90, isused to getter or scavenge hydrogen gas.

In U.S. Pat. No. 4,406,874 of William E. Wallace, F. Pourarian, and V.K. Sinha, for "ZrMn₂ -Type Alloy Partially Substituted WithCerium/Praseodymium/Neodymium and Characterized By AB₂ Stoichiometry"there is disclosed a thermochemical hydrogen storage alloy having theformula Zr_(x-1) M_(x) Mn₂ where x is between 0.0 and 0.3, and M is Ce,Pr, or Nd. The material is disclosed to have a hexagonal Laves structurewith the a crystallographic parameter equal to 5.00 to 5.03 Angstroms,and the c crystallographic parameter equal to 8.20 to 8.26 Angstroms.This alloy is disclosed to be a thermochemical hydrogen storage alloy.

All of the AB₂ hydrogen storage alloys described hereinabove are thermalhydrogen storage alloys. Prior art Laves phase-type electrochemicalhydrogen storage alloys are shown, for example, in Matsushita ElectricIndustrial Co. Ltd. Laid Open European Patent Application 0-293 660based on European Patent Application 88107839.8, filed May 16, 1988 andclaiming the priority dates of Japanese Patent Applications 87/119411,87/190698, 87/205683, 216898, and 87/258889, and the following Japanesepatents of Matsushita:

1. Japanese Patent 89-102855 issued Apr. 20, 1989, of Moriwaki, Gamo,and Iwaki, entitled HYDROGEN STORING ALLOY ELECTRODE, issued on JapanesePatent Application 87JP-258889, filed Oct. 14, 1987. This patentdiscloses multi-dimensional hydrogen storage alloys and their hydrides.The alloys are disclosed to be C₁₅ Laves phase type materials. Thematerials have the chemical formula expressed by A_(x) B_(y) Ni_(z)where A is Zr either alone or with one or more of Ti and Hf, the Ti orHf being 30 atomic percent or less, x=1.0, B is at least one of theelements Nb, Cr, Mo, Mn, Fe, Co, Cu, Al and rare earth elements such asLa and Ce, y=0.5 to 1.0, z=1.0 to 1.5, and the sum of y+z=1.5 to 2.5.Moriwaki et al disclose that this composition enhances the hydrogenstoring ability of the alloy and suppresses the loss of dischargecapacity which occurs after repeating charge/ discharge cycling (cyclelife) of Ti-Ni and Zr-Ni binary systems. There is no teaching of how onechoses between Nb, Cr, Mo, Mn, Fe, Co, Cu, Al, La and Ce or the relativeproportions within this class of substituents to optimize properties.

2. Japanese Patent 63-284758 of Gamo, Moriwaki, and Iwaki which issuedNov. 22, 1988 entitled HYDROGEN-STORING ELECTRODE on Japanese PatentApplication 62-119411 filed May 15, 1987. This patent discloses an alloywhich is expressed by a formula AB₂, and belongs to the Laves phase ofintermetallic compounds, with a cubically symmetric C₁₅ structure and acrystal lattice constant in the range from 6.92-7.70 angstroms. Arepresents one or more of the elements selected from among Ti, and Zr, Brepresents one or more elements selected from among V, and Cr. Thispatent is silent as to additional substituents or modifiers.

3. Japanese Patent 89-035863 of Gamo, Moriwaki, and Iwaki which issuedJan. 6, 1989 entitled HYDROGEN ABSORBING ELECTRODE on Japanese PatentApplication 62-190698 filed July 30, 1987. This patent discloses analloy of Zr, V, Ni satisfying the general formula ZrV_(a) Ni_(b), wherea=0.01-1.20, and b=1.0-2.5. However, this teaching of a general formuladoes not teach specific substituents or modifiers.

4. Japanese Patent 89-048370 of Gamo, Moriwaki, and Iwaki which issuedFeb. 22, 1989 entitled HYDROGEN ABSORBING ELECTRODE on Japanese PatentApplication 62-205683 filed August 19, 1987. i This patent discloses analloy ZrMo_(a) Ni_(b) where a=0.1-1.2, and b=1.1 2.5. This referencedoes not teach or suggest complex alloys of five or more components.

5. Japanese Patent 89-060961 of Gamo, Moriwaki, and Iwaki which issuedMar. 8, 1989 entitled HYDROGEN ABSORBING ELECTRODE on Japanese PatentApplication 62-216898 filed Aug. 31, 1987. This patent discloses ageneral alloy composition of the formula: Zr_(a) V_(b) Ni_(c) M_(d)where a, b, c, and d are the respective atomic ratios of elements Zr, V,Ni, and M, a=0.5 to 1.5, b=0.01 to 1.2, c=0.4 to 2.5, and d=0.01 to 1.8,and b+c+d=1.2 to 3.7, and M is one or more elements selected from Mg,Ca, Y, Hf, Nb, Ta, Cr, Mo, Ti, W, Mn, Fe, Co, Pb, Cu, Ag, Au, Zn, Cd,Al, In, Sn, Bi, La, Ce, Mm, Pr, Nd, and Th. This patents, with a list oftwenty eight metals plus misch metal, does not teach or even suggest anyrelationships between the members of the twenty eight metal class ofsubstituents.

The Laid Open European Patent Application of Gamo et al. describeshexagonal C₁₄ Laves phase materials characterized by lattice constantswith a from 4.8 to 5.2 Angstroms, and c from 7.9 to 8.3 Angstroms, andcubic C₁₅ Laves phase materials with a lattice constant from 6.92 to7.20 Angstroms. The materials have the formula AB_(a) where a isselected from a 16 member list of Zr, Ti, Hf, Ta, Y, Ca, Mg, La, Ce, Pr,Mm, Nb, Nd, Mo, Al, and Si, and B is selected from a 27 member list ofNi, V, Cr, Mn, Fe, Co, Cu, Zn, Al, Si, Nb, Mo, W, Mg, Ca, Y, Ta, Pd, Ag,Au, Cd, In, Sn, Bi, La, Ce and Mm, where A and B are different from eachother, and a is from 1.0 to 2.5.

The only guidance provided by Gamo et al. in the selection of the "A"components is that A be Zr, or a mixture of at least 30 atomic percentZr, balance one or more of Ti, Hf, Si, and Al. The only guidance withrespect to the "B" components is that B be V-Ni, Mo-Ni, or V-Ni-M inwhich M is another metal.

Gamo et al. describe with particularity the subclasses of Zr-V-Ni,Zr-Mo-Ni, and Zr-V-Ni-M (where M is chosen from Mg, Ca, Y, Hf, Nb, Ta,Cr, Mo, Mo, W, Mn, Fe, Co, Pd, Cu, Ag, Au, Zn, Cd, Al, Si, In, Sn, Bi,La, Ce, Mm, Pr, Nd, Th, and Sm). To be noted is that Ti containingmaterials are excluded from this sub-class, and that Gamo is silent asto any relationships and/or rules regarding the selection of themodifier or modifiers.

Another subclass disclosed by Gamo et al is A'B'Ni (where A' is Zr or atleast 30 atomic percent Zr with one or more of Ti, Hf, Al, and Si, andB' is one or more of V, Cr, Mn, Fe, Co, Cu, Zn, Al, Si, Nb, Mo, W, Mg,Ca, Y, Ta, Pd, Au, Ag, Cd, In, Sn, Bi, La, Ce, Mm, Pr, Nd, Th, and Sm.Gamo et al disclose that when A' is Zr, the Zr is preferably incombination with Al or Si, and preferably B' represents two or moreelements from the group consisting of Cr, Mn, Fe, and Co. What Gamofails to disclose is a modified, five or more component material basedupon Ti-V-Zr-Ni-Cr, with additional metallic components to increase oneor more of cycle life, cell voltage, capacity, discharge ratecapability, or low temperature performance.

C. BACKGROUND OF THE INVENTION: Ti-V-Zr-Ni TYPE MATERIALS

Another suitable class of electrochemical hydrogen storage alloys arethe Ti-V-Zr-Ni type active materials for the negative electrode. Thesematerials are disclosed in U.S. Pat. No. 4,551,400 to Krishna Sapru,Kuochih Hong, Michael A. Fetcenko, and Srinivasan Venkatesan,incorporated herein by reference. These materials reversibly formhydrides in order to store hydrogen. The materials of Sapru et al havethe generic Ti-V-Zr-Ni composition, where at least Ti, V, and Ni arepresent with at least one or more of Cr, Zr, and Al. The materials ofSapru et al are multiphase materials, which may contain one or morephases of the AB₂ type, with C₁₄ and C₁₅ type structures. Onecomposition disclosed by Sapru is:

    (TiV.sub.2-x Ni.sub.x).sub.1-y M.sub.y

where x is between 0.2 and 1.0, y is between 0.0 and 0.2, and M=Al orZr. Two other illustrative compositions of Sapru et al illustrate thepartial substitution of the Ti by one or both of Zr and Cr:

    Ti.sub.2-x Zr.sub.x V.sub.4-y Ni.sub.y

where zirconium is partially substituted for Ti, x is between 0.0 and1.5, and y is between 0.6 and 3.5; and

    Ti.sub.1-x Cr.sub.x V.sub.2-y Ni.sub.y

where chromium is partially substituted for Ti, x is between 0.0 and0.75, and y is between 0.2 and 1.0. It is of course to be understoodfrom the teachings of Sapru et al that both zirconium and chromium maybe partially substituted for titanium. Generally,

    (Ti+Zr+Cr)/(V+Ni)

is from about 0.40 to about 0.67 to retain the proper Ni morphology inthe hydrogen storage alloy.

Sapru et al, however, are silent as to the effects of additives andmodifiers beyond those enumerated above, and as to the interactionsbetween these additives and modifiers.

Other Ti-V-Zr-Ni materials may also be used for the rechargeablehydrogen storage negative electrode. One such family of materials arethose described in U.S. Pat. No. 4,728,586 of Srini Venkatesan, BenjaminReichman, and Michael A. Fetcenko for ENHANCED CHARGE RETENTIONELECTROCHEMICAL HYDROGEN STORAGE ALLOYS AND AN ENHANCED CHARGE RETENTIONELECTROCHEMICAL CELL, the disclosure of which is hereby incorporatedherein by reference. Venkatesan et al. describe a specific sub-class ofthe Ti-V-Ni-Zr hydrogen storage alloys comprising titanium, vanadium,zirconium, nickel, and a fifth component, chromium. In a particularlypreferred exemplification of Venkatesan et al. the hydrogen storagealloy has the composition (Ti₀.33-x Zr_(x) V₀.67-y Ni_(y))_(1-z) Cr_(z)where x is from 0.00 to 0.25, y is from 0.1 to 0.6, and z is aneffective amount for electrochemical charge retention, generally greaterthen 0.05 and less then 0.20, and preferably about 0.07. The alloys maybe viewed stoichiometrically as 80 atomic percent of an V-Ti-Zr-Nimoiety and up to 20 atomic percent of Cr, where the ratio of(Ti+Zr+Cr+optional modifiers) to (Ni+V+optional modifiers), is between0.40 and 0.67. Venkatesan et al, while mentioning the possibility ofadditives and modifiers beyond the Ti, V, Zr, Ni, and Cr components ofthe alloys, are silent as to the specific additives and modifiers, andthe amounts and interactions of the modifiers and the particularbenefits that would be expected therefrom.

A strong motivation for using the above described V-Ti-Zr-Ni family ofelectrochemical hydrogen storage alloys, as described by Sapru et al.,and Venkatesan et al., including the Ti-V-Zr-Ni-Cr hydrogen storagealloys of Venkatesan et al., is the inherently higher discharge ratecapability of these materials. Important physical properties in thisregard are the substantially higher surface areas for the V-Ti-Zr-Nimaterials, and the metal/electrolyte interface. Measured in surfaceroughness factor (total surface area divided by geometric surface area),the V-Ti-Zr-Ni materials can have roughness factors of about 10,000. Thevery high surface area plays an important role in the inherently highrate capability of these materials.

The metal/electrolyte interface also has a characteristic surfaceroughness. The characteristic surface roughness for a given negativeelectrode electrochemical hydrogen storage material is important becauseof the interaction of the physical and chemical properties of the hostmetals, as well as of the alloys and crystallographic phases thereof, inan alkaline environment. The microscopic chemical, physical, andcrystallographic parameters of the individual phases within the hydrogenstorage alloy material are believed to be important in determining themacroscopic electrochemical characteristics of the hydrogen storagematerial. Since all of the elements, as well as many alloys and phasesthereof, are present throughout the metal, they are also represented atthe surfaces and at cracks which form the metal/electrolyte interface.

In addition to the physical nature of the roughened surface, it has beenobserved that the V-Ti-Zr-Ni materials tend to reach a steady statesurface condition and particle size. This steady state surface conditionis characterized by a relatively high concentration of metallic nickel.These observations are consistent with a relatively high rate of removalof the oxides of titanium and zirconium from the surface and a muchlower rate of nickel solubilization. The resultant surface seems to havea higher concentration of nickel than would be expected from the bulkcomposition of the negative hydrogen storage electrode. Nickel in themetallic state is electrically conductive and catalytic, imparting theseproperties to the surface. As a result, the surface of the negativehydrogen storage electrode is more catalytic and conductive than if thesurface contained a higher concentration of insulating oxides.

The surface, having a conductive and catalytic component, e.g., themetallic nickel, appears to interact with chromium, including chromiummetal, chromium compounds, and chromium alloys, in catalyzing varioushydride and dehydride reaction steps. To a large extent, many electrodeprocesses, including competing electrode processes, are controlled bythe presence of chromium in the hydrogen storage alloy material, asdisclosed in the aforementioned U.S. Pat. No. 4,728,586 of SriniVenkatesan, Benjamin Reichman, and Michael A. Fetcenko for ENHANCEDCHARGE RETENTION ELECTROCHEMICAL HYDROGEN STORAGE ALLOYS AND AN ENHANCEDCHARGE RETENTION ELECTROCHEMICAL CELL, the disclosure of which wasincorporated herein by reference.

Another reference which discusses the Ti-V-Zr-Ni class of materials isU.S. Pat. No. 4,849,205 to Kuochih Hong for "HYDROGEN STORAGE HYDRIDEELECTRODE MATERIALS". The Hong patent discloses four separate types ofmaterials, each having four or five components. More particularly, Hongdiscloses a first material having the formula Ti_(a) Zr_(b) Ni_(c)Cr_(d) Mx, wherein 0.1 a 1.4; 0.1 b 1.3; 0.25 c 1.95; 0.1 d 1.4; 0.0 x0.20; a+b+c+d=3; and M Al, Si, V, Mn, Fe, Co, Cu, Nb and Ln's. In thissystem, Hong teaches exemplary compounds primarily having fourcomponents including Ti-Zr-Ni-Cr, with Cr up to 17% of the material. Theone five component exemplary material taught by Hong included Mn inconcentrations of approximately 3.2%. No other exemplary five componentcompounds are taught by Hong. More importantly, the only documentedbenefit of the exemplary alloys of formula one are their enhanced chargecapacity. However, a careful perusal of Table 1 of the Hong referenceshows that the inclusion of Mn in the four component material of Formula1 reduces the charge capacity of those materials. Further, while otherbenefits of the Formula 1 materials are suggested, i.e., long lifecycles, there is no documented evidence of improvemented life cycle,much less any other operational parameter. Thus, one of ordinary skillwould in fact be taught away from the use of Mn in a metal-hydridebattery system since its inclusion reduces the charge capacity of thematerials, and no other apparent benefits thereof result. Additionally,the use of other modifier materials in the basic four component systemof Formula 1 is never even considered either in light of charge capacityor any other operational parameter. Therefor, there is no indication ofwhat, if any benefit would result therefrom.

The second class of materials taught by Hong is expressed by the formulaTi_(a) Cr_(b) Z_(c) Ni_(d) V_(3-1-b-c-d) M_(x) ; wherein 0.1≦a≦1.3;0.1≦b≦1.2; 0.1≦c≦1.3; 0.2≦d≦1.95; 0.4≦a+b+c+d≦2.9; 0.00≦x≦0.2; and M=Al,Si, Mn, Fe, Co, Cu, Nb, Ln's. In this class, Hong teaches exemplarycompounds primarily having five components including Ti-Zr-Ni-Cr-V. Theone six component exemplary material taught by Hong includes Cu as amodifier element in concentrations of approximately 3.2%. No otherexemplary six component compounds are taught by Hong. More importantly,the only documented benefit of the exemplary alloys of Formula 2, likethat of Formula 1, are their enhanced charge capacity. However, acareful perusal of Table 1 of the Hong reference shows that theinclusion of Cu in the five component material of Formula 2 displaysreduced charge capacity compared to other five component materials.Further, while other benefits of the Formula 2 materials are suggested,i.e., long life cycles and good rate capability, there is no documentedevidence of improvemented life cycle or rate capability, much less anyother operational parameter. Thus, one of ordinary skill would in factbe taught away from the use of Cu in a metal-hydride battery systemsince its inclusion reduces the charge capacity of the materials, and noother apparent benefits thereof result. Additionally, the use of othermodifier materials in the basic five component system of Formula 2 isnever even considered either in light of charge capacity or any otheroperational parameter. Therefore, there is no indication of what, if anybenefit would result therefrom.

The third class of materials taught by Hong is expressed by the formula:Ti_(a) Zr_(b) Ni_(c) V_(3-a-b-c) M_(x) wherein 0.1≦a≦1.3; 0.1≦b1.3;0.25≦c≦1.95; 0.6≦a+b+c≦2.9; 0.0≦x≦0.2; and wherein if x=0, a+b does notequal 1.0, and 0.24 b 1.3. Further, M=Al, Si, Cr, Mn, Fe, Co, Cu, Nb,Ln's. In this class of materials, Hong teaches exemplary compoundsprimarily having four components including Ti-Zr-Ni-V. The one fivecomponent exemplary material taught by Hong included Cu as a modifierelement in concentrations of approximately 6.2%. No other exemplary fivecomponent compounds are taught by Hong. More importantly, the onlydocumented benefit of the exemplary alloys of Formula 3, are theirenhanced charge capacity. However, a careful perusal of Table 1 of theHong reference shows that the inclusion of Cu in the four componentmaterial of Formula 3 displays significantly reduced charge capacitycompared to other four component materials disclosed therein. Further,no other benefits of the Formula 3 materials are suggested, either withor without the inclusion of Cu as a modifier component. Thus, there canbe no doubt but that one of ordinary skill would avoid the use of Cu ina metal-hydride battery system since its inclusion so significantlyreduces the charge capacity of the materials, without contributing anyapparent benefits thereof. Additionally, the use of other modifiermaterials in the basic four component system of Formula 3 is never evenconsidered either in light of charge capacity or any other operationalparameter. Therefore, there is no indication of what, if any benefitwould result therefrom, nor any reason for the use thereof suggested.

Finally, the fourth class of materials taught by Hong can be representedby the formula: Ti_(a) Mn_(b) V_(c) Ni_(d) M_(x) wherein 0.1≦a≦1.6;0.1≦b≦1.6; 0.1≦c≦1.7; 0.2≦d≦2.0; a+b+c+d=3; 0.0≦x≦0.2; and M=Al, Si, Cr,Mn, Fe, Co, Cu, Nb, Ln's. In this class of materials, Hong teachesexemplary compounds primarily having four components includingTi-Mn-Ni-V. The one five component exemplary material taught by Hongincluded Co as a modifier element in concentrations of approximately3.2%. No other exemplary five component compounds are taught by Hong.More importantly, the only documented benefit of the exemplary alloys ofFormula 4, are their enhanced charge capacity. However, a carefulperusal of Table 1 of the Hong reference shows that the inclusion of Coin the five component material of Formula 4 displays, once again,significantly reduced charge capacity compared to other materialsdisclosed therein. Further, no other benefits of the Formula 4 materialsare suggested, either with or without the inclusion of Co as a modifiercomponent. Thus, there can be no doubt but that one of ordinary skillwould avoid the use of Co in a metal-hydride battery system since itsinclusion so significantly reduces the charge capacity of the materials,without contributing any apparent benefits thereto. Additionally, theuse of other modifier materials in the basic four component system ofFormula 4 is never even considered either in light of charge capacity orany other operational parameter. Therefore, there is no indication ofwhat, if any benefit would result therefrom, nor any reason for the usethereof suggested.

It is important to note that while Hong discloses a rather lengthy"laundry list" of possible modifier materials, only two can truly beconsidered modifiers, Cu and Co since the addition of Mn is clearlytaught in the materials of class four. Yet, no benefit is shown from Cuand Co modification. In fact, Hong teaches away from these modifierssince he only demonstrates capacity improvement, and Cu and Co asmodifiers substantially reduce capacity. In addition, Hong is silent asto any intended functions of any components. Since the remainingmodifier materials disclosed by Hong are neither employed in exemplarycompounds, nor are discussed in light of their possible benefits, it canonly be concluded that the teaching value of the Hong "laundry list" isminimal at best. This is because one of ordinary skill in the art wouldnot know the possible advantages to be expected from using other ones ofsaid modifier materials or indeed the benefits of employing severalmodifier materials together in one alloy.

D. BACKGROUND OF THE INVENTION: AB₅ TYPE HYDROGEN STORAGE ALLOYS

An alternative class of hydrogen storage alloys are the AB₅ typehydrogen storage alloys. These alloys differ in chemistry,microstructure, and electrochemistry from the AB₂ and V-Ti-Zr-Ni-Crtypes of electrochemical hydrogen storage alloys. Rechargeable batteriesutilizing AB₅ type negative electrodes are described, for example, in(i) U.S. Pat. No. 3,874,928 to Will for "Hermetically Sealed SecondaryBattery With Lanthanum Nickel Electrode", (ii) U.S. Pat. No. 4,214,043to Van Deuketom for "Rechargeable Electrochemical Cell", (iii) U.S. Pat.No. 4,107,395 to van Ommering et al. for "Overchargeable Sealed MetalOxide/Lanthanum Nickel Hydride Battery," (iv) U.S. Pat. No. 4,107,405 toAnnick Percheron born Guegen et al for "Electrode Materials Based OnLanthanum and Nickel, and Electrochemical Uses of Such Materials," (v)U.S. Pat. No. 4,112,199 to James D. Dunlop et al for "Lanthanum NickelHydride-Hydrogen/Metal Oxide Cell," (vi) U.S. Pat. No. 4,125,688 toBonaterre for "Negative Electrodes for Electric Cells" which disclosesHg modified LaNi₅ negative electrodes, (vii) U.S. Pat. No. 4,214,043 tovon Dueketom for "Rechargeable Electrochemical Cell" which shows aLaNi₅ - Ni cell, (viii) U.S. Pat. No. 4,216,274 to Bruning for "BatteryWith Hydrogen Absorbing Material of the Formula LaM₅," which arechargeable cell with an AB₅ type negative electrode of the formulaLaM₅ where M is Co or Ni; (ix) U.S. Pat. No. 4,487,817 to Willems et al.for "Electrochemical Cell Comprising Stable Hydride Forming Material"discloses an AB₅ type material where A is chosen from mischmetal, Y, Ti,Hf, Zr, Ca, Th, La, and the rare earths, in which the total of Y, Ti,Hf, and Zr is less than 40% of the A component, and B is chosen from twoor more members of the group of Ni, Cu, Co, Fe, and Mn, and at least onemember of the group Al, Cr, and Si, (x) U.S. Pat. No. 4,605,603 to Kandaet al for "Hermetically Sealed Metallic Oxide-Hydrogen Battery UsingHydrogen Storage Alloy" discloses an AB₅ type electrochemical hydrogenstorage alloy having the formula MNi₅₋(x+y) Mn_(x) Al_(y), where M ischosen from the group consisting of lanthanum, lanthanides, andmischmetals, x and y are each between 0.0 and 1.0, and x+y is between0.2 and 1.0; (xi) U.S. Pat. No. 4,621,034 to Kanda et al for "SealedMetal Oxide- Hydrogen Storage Cell" discloses a LaNi₅ cell where the Niis partially substituted by Al and/or Mn, (xii) U.S. Pat. No. 4,696,873to Yagasaki et al for "Rechargeable Electrochemical Cell With A NegativeElectrode Comprising A Hydrogen Absorbing Alloy Including Rare EarthComponent" discloses AB₅ type alloys of the Mischmetal-Ni-Mn-Al type,(xiii) U.S. Pat. No. 4,699,856 to Heuts et al for "Electrochemical Cell"discloses an AB₅ type material where A is chosen from mischmetal, Y, Ti,Hf, Zr, Ca, Th, La, and the rare earths, in which the total of Y, Ti,Hf, and Zr is less than 40% of the A component, and B is chosen from twoor more members of the group of Ni, Cu, Co, Fe, and Mn, and at least onemember of the group Al, Cr, and Si, and including an activator from thegroup consisting of Ni, Pd, Pt, Ir, and Rh.

It is clear from the above cited documents that the AB₅ type alloys area distinct and specific class of materials. Extensive work on processingtechniques and electrode and cell design demonstrate that thesingularity of AB₅ technology, that is, that the AB₅ technologyrepresents a separate field of inventive effort from the AB₂ andV-Ti-Zr-Ni-Cr classes of alloys. In particular, modifications of AB₅type alloys must be viewed as practical only within the specific AB₅type structure. This is due to the unique metallurgical,electrochemical, and oxidation characteristics of the AB₅ class ofalloys, especially regarding the use of lanthanum and other rare earthsfor electrochemical applications. Even for the AB₅ alloys, thedisclosure of the selection and role of modifiers generally, and even ofspecific modifiers for specific performance aspects, is vague andnon-specific.

E. BACKGROUND OF THE INVENTION: DEFICIENCIES OF THE PRIOR ART

While the prior art hydrogen storage alloys frequently utilized variousindividual modifiers and combinations of modifiers to enhanceproperties, there was no clear teaching of the role of an individualmodifier, or of the interaction of that modifier with other componentsof the alloy, or of the effects of the modifiers on properties.

For electrochemical applications, which are substantially different fromthermal hydrogen storage applications, one must consider all performanceattributes, such as cycle life, high rate discharge, discharge voltage,polarization, self discharge, low temperature capacity, and lowtemperature voltage.

While it is desirable to have alloys with all of these characteristics,it may also be advantageous to emphasize specific properties for a givenapplication.

The prior art is also deficient in specifying the role of particularmodifications, much less in how they work. Frequently with AB₂ and AB₅type materials, there is a modifier, X, where X is the rest of thePeriodic Chart. Certainly prior art references of this type teach awayfrom specific roles and functions of materials, and provide no practicalbenefit.

SUMMARY OF THE INVENTION

According to the invention disclosed and claimed herein, it has beenfound that subtle changes in the local chemical and structural order ofthe Ti-V-Zr-Ni type hydrogen storage alloys, including Ti-V-Zr-Ni-Cralloys, for example changes in composition within one or more phasesoccuring through the addition of modifiers, have significant effects onthe macroscopic electrochemical properties of negative electrodesincorporating these hydrogen storage alloys. According to the invention,the subtle interactions of individual metallic substituents in theTi-V-Zr-Ni type structure (including the Ti-V-Zr-Ni-Cr typeelectrochemical hydrogen storage alloy materials) are engineered tomaximize desirable electrochemical properties of the hydrogen storagealloy, while minimizing undesirable electrochemical properties thereof.

According to the invention disclosed herein, subtle changes instoichiometry are utilized to effect these macrocopic changes. Forexample, starting with the composition V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇, disclosedin the commonly assigned Venkatesan et al. patent, we have made subtlemodifications in the stoichiometry thereof, developing such materialsas:

(V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇)₉₅ Al₅,

(V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇)₉₅ Mn₅,

(V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇)₉₅ Mo₅,

(V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇)₉₅ Cu₅,

(V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇)₉₅ W₅,

(V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇)₉₅ Fe₅,

(V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇)₉₅ Co₅,

V₂₂ Ti₁₆ Zr₁₆ Ni₃₂ Cr₇ Co₇,

V₂₀.6 Ti₁₅ Zr₁₅ Ni₃₀ Cr₆.6 Co₆.6 Mn₃.6 Al₂.7, and

V₂₂ Ti₁₆ Zr₁₆ Ni₂₇.8 Cr₇ Co₅.9 Mn₃.1 Al₂.2,

where we have been able to provide enhanced properties therein withrespect to the same properties in V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇. Thus,according to our invention, it is possible to do one or more ofincreasing cycle life (number of charge-discharge cycles at constantdrain rate with constant cell capacity), increasing the specificcapacity (amp-hours per unit volume or per unit mass), increasing themid-point voltage at various discharge rates, decreasing thepolarization at various discharge rates, increasing the low temperaturespecific capacity, increasing the low temperature mid-point voltage,decreasing the low temperature polarization, or decreasing the the selfdischarge rate.

While the above description characterizes the macroscopic improvementsto the functioning electrode and cell, it is also possible tocharacterize the more precise function of the modified compositions. Forexample, an inventive alloy may have one or more of the followingfunctions or attributes:

1. An increase in the active surface area.

2. An increased surface catalytic activity to provide one or more of:

a. decreased metal oxidation,

b. enhanced O₂ recombination.

3. A surface oxide or film which is:

a. of controlled thickness, i.e., thicker or preferably, thinner,

b. of controlled conductivity, i.e, lower or, preferably, higherconductivity.

4. Decreased corrosion of one or more elements of the alloy.

5. Provides an oxide which allows, catalyzes, or enhances activation.

6. Provide an oxide which precipitates species which:

a. inhibit corrosion of other species;

b. decrease oxygen evolution at the positive electrode by increasing theO₂ overvoltage thereof;

c. protect the Ni hydroxide electrode from other corrosion species ormechanisms which can promote oxygen evolution, and/or decrease chargeefficiency, and/or lower cell capacity.

7. Increase hydrogen storage capacity and/or hydrogen utilization.

8. Modify intergranular phase composition, structure, or proportions.

9. Improve bulk diffusion in the metal hydride, for example, bymodification of phase composition, structure, or proportion.

10. Lower the heat of formation of the M-H bond, thereby increasing thedischarge voltage of the metal hydride electrode.

11. Improve bulk diffusion and/or catalysis in the metal hydride throughmodification of grain compositions, microstructure, or grain boundarieswithin the multiphase material.

For example, each of the above identified modifications of V₂₂ Ti₁₆ Zr₁₆Ni₃₉ Cr₇ has certain unique advantages with respect thereto. Theseinclude:

1. (V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇)₉₅ Al₅, modified by the addition of a smallamount of aluminum exhibits high specific capacity (342 mAh/g), highermidpoint voltage on discharge, decreased internal resistance in a sealedcell, and enhanced low temperature properties, i.e., low temperaturecapacity and low temperature mid-point voltage;

2. (V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇)₉₅ Mn₅, modified by the addition of a smallamount of manganese, exhibits enhanced discharge voltage, high specificcapacity (355 mAh/g), improved cycle life, decreased IR loss in a sealedcell, decreased IR loss in a half cell, and enhanced low temperatureproperties, i.e., enhanced low temperature capacity and low temperaturemid-point voltage;

3. (V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇)₉₅ Mo₅, modified by the addition of a smallamount of molybdenum, exhibits decreased IR loss in a half cell,decreased IR loss in a sealed cell, and enhanced mid-point voltage;

4. (V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇)₉₅ Cu₅, modified by the addition of a smallamount of copper, exhibits high specific capacity (333 mAh/g), improvedcycle life, decreased IR loss in a sealed cell, and decreased IR loss ina half cell;

5. (V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇)₉₅ W₅, modified by the addition of a smallamount of tungsten, exhibits high specific capacity (320 mAh/g),enhanced mid-point voltage, decreased IR loss in a sealed cell, andenhanced low temperature capacity;

6. (V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇)₉₅ Fe₅, modified by the addition of a smallamount of iron, exhibits high specific capacity (355 mAh/g), vastlyenhanced cycle life, decreased half cell IR loss, enhanced mid-pointvoltage and low temperature properties, such as low temperature capacityand low temperature mid-point voltage;

7. (V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇)₉₅ Co₅, modified by the addition of a smallamount of cobalt, exhibits high specific capacity (349 mAh/g), improvedcycle life, decreased half cell IR loss, decreased sealed cell IR loss,and enhanced low temperature mid-point voltage;

8. V₂₂ Ti₁₆ Zr₁₆ Ni₃₂ Cr₇ Cr₇ Co₇, which is similar to (V₂₂ Ti₁₆ Zr₁₆Ni₃₉ Cr₇)₉₅ Co₅, above, but clearly demonstrates the importance of theamount of modifier, what the modifier substitutes for, and theparticular intent of the modification. This material exhibits highspecific capacity (329 mAh/g), vastly improved cycle life, decreasedhalf cell IR loss, and enhanced room temperature mid-point voltage andlow temperature mid-point voltage;

9. V₂₀.6 Ti₁₅ Zr₁₅ Ni₃₀ Cr₆.6 Co₆.6 Mn₃.6 Al₂. 7 having superior cyclelife (including flooded cycle life), enhanced mid-point voltage,enhanced low temperature capacity, enhanced low temperature voltage,decreased sealed cell IR loss, and decreased half cell IR loss.

10. V₂₂ Ti₁₆ Zr₁₆ Ni₂₇.8 Cr₇ Co₅.9 Mn₃.1 Al₂.2 which exhibits highspecific capacity, high midpoint voltage, high voltage at lowtemperatures, decreased sealed cell IR losses, and vastly improved cyclelife.

The negative electrode is formed of the modified, multicomponent,multiphase, reversible electrochemical hydrogen storage alloy of theinvention. This electrode is capable of reversibly electrochemicallycharging and discharging hydrogen in alkaline aqueous media.

The compositionally and structurally modified, high performance,electrochemical hydrogen storage negative electrode is incorporated intoa sealed, rechargeable electrochemical cell, i.e., a secondary cell. Theelectrochemical cell includes a container, e.g., a sealed container,containing positive and negative electrodes in an electrolyte andseparated from one another by a separator.

Typically the positive electrode is a nickel hydroxide electrode, andthe separator may be non-woven nylon, e.g., with a thickness of about0.0085 inches. The electrolyte is a concentrated aqueous alkalineelectrolyte, e.g., containing at least about 30 percent KOH.

THE FIGURES

The present invention can be more completely understood by reference tothe accompanying drawings in which:

FIG. 1 is a sectional side view of a flat electrochemical cell; and

FIG. 2 is a sectional side view of a jelly-roll electrochemical cell.

FIG. 3 is plot of half cell cycle life, i.e., capacity versus cyclenumber, for half cells having electrodes fabricated of V₂₂ Ti₁₆ Zr₁₆Ni₃₉ Cr₇ (control), and V₂₀.6 Ti₁₅ Zr₁₅ Ni₃₀ Cr₆.6 Co₆.6 Mn₃.6 Al₂.7(modified in accordance with the invention) as described in Example VI.

FIGS. 4-1 through 4-8 are plots of cycle life, i.e., capacity versuscycle number, for sealed cells. In FIG. 6-1 the cell is a control cellwith a prior art electrode. In FIG. 4-2 through 4-8 the cells havemodified electrodes, as described in Example VII.

FIGS. 5-1 through 5-3 are plots of parts per million vanadium in theelectrolyte versus time for a control electrode material and a modifiedelectrode material.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, there is provided a family ofhydrogen storage alloys, derived from the V-Ti-Zr-Ni and V-Ti-Zr-Ni-Cralloys of Sapru et al and Venkatesan et al, in which the V, Ti, Zr, Ni,and Cr are partially replaced, either individually or as a group, by oneor more elemental modifiers, and the alloy has the nominal composition:

    (V.sub.4-y Ni.sub.y Ti.sub.2-x Zr.sub.x Cr.sub.z).sub.a M'.sub.b M".sub.c M.sub.d.sup.iii

where x is between 0 and 1.5, y is between 0.6 and 3.5, z is between0.00 and 1.44, a designates that the V-Ni-Ti-Zr-Cr component as a groupis from 70 to 100 atomic percent of the alloy, and b,c,d,e, . . . , aremodifiers which may be individually or collectively up to 30 atomicpercent of the total alloy, and M', M", M^(iii), and M^(iv) are chosenfrom Al, Mn, Mo, Cu, W, Fe, Co, and combinations thereof, as will bemore fully described hereinbelow. It is, of course, to be understood,that the stoichiometric coefficients in the above nominal formulaactually encompass a range of homogeneity, with the coefficient on theV, 4-y, actually being within the range of 3.6-y to 4.4-y, as long asvanadium and nickel are both present in the composition, and with thecoefficient on the Ti, 2-x, actually being within the range of 1.8-x to2.2-x, as long as titanium and zirconium are both present in thecomposition. Thus, the nominal composition may be represented by theformula:

    (V.sub.y'-y Ni.sub.y Ti.sub.x'-x Zr.sub.x Cr.sub.z).sub.a M'.sub.b M".sub.c M.sub.d.sup.iii

where x, y, z, a, b, c, d, e, M', M", M^(iii), and M^(iv) are as definedabove, x' is between 1.8 and 2.2, and y' is between 3.6 and 4.4.

For simplicity sake, and for practical application, the modifiers aredemonstrated with the composition V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇, which wasspecifically disclosed and claimed in U.S. Pat. No. 4,728,586 toVentakesan et al., of record. This particular composition has shownexcellent overall electrochemical properties. While the modifiers havebeen demonstrated to function on this composition as (V₂₂ Ti₁₆ Zr₁₆ Ni₃₉Cr₇)₉₅ M₅, where M is one or more of Al, Co, Mn, Fe, W, Cu, Mo, andcombinations thereof, it should also be understood that the modifieraccentuates performance outside of this stoichiometry as demonstrated byV₂₂ Ti₁₆ Zr₁₆ Ni₃₂ Cr₇ Co₇ where Co was preferentially substituted forNi to emphasize cycle life.

Further, while modifiers have been shown at a level of 5 to 13 atomicpercent, it is to be noted that the modifier may be used at an effectivelevel below five atomic percent, and as a group modifiers may be used upto thirty atomic percent, or even higher, of the alloy. It will be shownhereinbelow that the functionality of a modifier can be predicted, andthe concentration of a particular modifier will result in theenhancement of a specific parameter.

Consequently it should be understood that while modifiers are moresimply written as:

    (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7a).sub.b M'.sub.c M".sub.d M.sup.iii M.sup.iv.sub.3. . .

the invention herein contemplated and described includes compositionshaving the more general formula

    (V.sub.y'-y Ni.sub.y Ti.sub.x'-x Zr.sub.x Cr.sub.z).sub.a M'.sub.b M".sub.c M.sub.d iii. . .

It is, of course, to be understood that where specific compositions aregiven, other compositions with like properties and within thehomogeneity range thereof are encompassed thereby.

In a preferred exemplification the principle modifier is Co. In a stillfurther and particularly preferred exemplification, the alloy comprisesthe primary modifier, Co, which partially substitutes for Ni only, andpartially substitutes for V-Ti-Zr-Ni-Cr, and other modifiers such as Aland Mn. One particularly preferred family of hydrogen storage alloys arethe V-Ti-Zr-Ni-Cr-Co-Mn-Al class of alloys, exemplified by V₂₀.6 Ti₁₅Zr₁₅ Ni₃₀ Cr₆.6 Co₆.6 Mn₃.6 Al₂.7 where the Co partially substitutes forNi, and partially substitutes for V-Ti-Zr-Ni-Cr, and the Mn and Al bothpartially substitute for V-Ti-Zr-Ni-Cr as well. The above describedmodifications and substitutions result in other particularly preferredalloys and families of alloys, such as V-Ti-Zr-Ni-Cr-Co, andV-Ti-Zr-Ni-Cr-Fe, as well as V-Ti-Zr-Ni-Cr-Co-Mn-Al,V-Ti-Zr-Ni-Cr-Co-Mn-Al-Fe, and V-Ti-Zr-Ni-Cr-Co-Fe. Moreover, it is tobe understood that in the system V-Ti-Zr-Ni-Cr-Co the Co may substitutefor either V-Ti-Zr-Ni-Cr, or Ni, or both V-Ti-Zr-Ni-Cr and Ni.

As is well known in the rechargeable battery art, the introduction of anew system, e.g., rechargeable batteries utilizing metal hydridenegative electrodes, is promoted as the electrochemical propertiesthereof are enhanced. Thus, there is motivation to improve properties,such as, specific capacity, midpoint voltage, polarization, lowtemperature voltage and capacity, and, particularly, cycle life.

There are many methods and design expedients commonly used inelectrochemistry to enhance performance. These methods are relevant tomost systems. For example, cell capacity is increased by betterutilization of active material, special cell designs to incorporate moreactive material, and even sacrifice of other properties. Midpointdischarge voltage may be improved by better current collection, higherelectrode surface area, special surface treatments, and optimizedporosity and pore size. Some of the same methods described with respectto improving mid-point discharge voltage may also be used to improve lowtemperature behavior. The improvement of low temperature properties mayalso include modification of the electrolyte. Cycle life is aparticularly important characteristic, and frequently cycle lifeproblems are materials related. Specific improvements are generallyspecific for and directed to a particular system.

Researchers working in the field of nickel hydride negative electrodesin nickel- metal hydride cells have long sought to enhance theperformance of these cells. There is extensive prior art showing:

The use of foam substrates and/or pasted nickel hydroxide positiveelectrodes to increase capacity.

Special metal hydride powder fabrication methods to increase surfacearea.

Special metal hydride coatings of the powder and electrode, to improvecycle life.

Special powder and electrode pretreatments to assist activation.

Special separators to reduce self-discharge and improve cycle life.

Negative electrode construction requiring binders to assist cycle life.

While these techniques and expedients have shown improvements, it isclear that many of these methods, techniques and expedients are designedto compensate for shortcomings in the basic materials used as the metalhydride. At the very least, improvements in the basic electrodematerials can be used in conjunction with these other methods,techniques, and expedients to improve performance.

The invention described and claimed herein deals with improvedelectrochemical performance through basic improvement of the hydrogenstorage alloys. The modified alloys described and claimed herein haveone or more of the following features or attributes:

1. An increase in the active surface area.

2. An increased surface catalytic activity to provide one or more of:

a. decreased metal oxidation,

b. enhanced O₂ recombination.

3. A surface oxide or film which is:

a. of controlled thickness, i.e., thicker or thinner,

b. of controlled conductivity, i.e, higher or lower conductivity.

4. Decreased corrosion of one or more elements of the alloy.

5. An oxide which allows, catalyzes, or enhances activation.

6. An oxide which precipitates species that:

a. inhibit corrosion of other species;

b. decrease oxygen evolution at the positive electrode by increasing theO₂ overvoltage thereof;

c. protect the Ni hydroxide electrode from other corrosion species ormechanisms which can promote oxygen evolution, and/or decrease chargeefficiency, and/or lower cell capacity.

7. An increased hydrogen storage capacity and/or hydrogen utilization.

8. A modified intergranular phase composition, structure, orproportions.

9. Improved bulk diffusion in the metal hydride, by, for example,modification of phase composition, structure, or proportion.

10. Reduced heat of formation of the M-H bond, thereby increasing thedischarge voltage of the cell.

11. Improvement in one or more of bulk diffusion or catalysis in themetal hydride through modification of one or more of grain compositions,microstructure, or grain boundaries within the multiphase material.

Some of the modifiers, such as Al, Mn, Cu, W, Fe, Co, and combinationsof one or more of Co, Mn, and Al, improve electrochemical specificcapacity. For the V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇ alloy, the typical capacity isabout 320 milliampere hours per gram (mAh/g) of active material. Theabove mentioned modifiers raise the specific capacity to as high as 355mAh/g. This is shown for Mn and Fe in Example 1.

Though not wishing to be bound by this or any specific theory, it isbelieved that the higher specific capacity is obtained through improvedcatalysis. None of the modifiers is a hydride former underelectrochemically useful conditions. In fact, by dilution, the hydrideforming elements, V, Ti, and Zr, are actually reduced in concentrationin the alloy. It is believed that instead of actually storing morehydrogen, the modifiers increase the utilization of available hydrogen.This may be due to improved hydrogen bulk diffusion through the alloy orthrough grain boundaries, higher surface area, or surface conditionsallowing more complete charge and/or discharge. Even though testing isdone at low charge and discharge rates, the improvement in specificcapacity may be related to improved rate capability. The modifier'sfunction may be weakening the M-H bond within particular phases,providing less distinct grain boundaries, metallurgically providinghigher surface are, and/or electrochemically providing a surface withmore porosity, higher conductivity, and/or more catalytic activity.Moreover, by raising the discharge voltage, the capacity may be enhancedsince capacity is measured to a specific cutoff voltage.

Some of the modifiers improve discharge rate capability, improving oneor more of: higher midpoint voltage on discharge, decreased polarizationduring flooded half-cell testing, or lower internal resistance whentested in a sealed cell. Appropriate modifiers for this purpose are Al,Mn, Mo, Cu, W, Fe, Co, and the combination of Co, Mn, and Al. Magnitudesof improvement range from a 50 mV to 100 mV increase in midpoint voltageat a 2 amp discharge rate for aa C size cell, a 40 percent decrease inhalf cell polarization, and a 28 percent reduction in sealed cellinternal resistance. It should be noted that internal resistance denotesvoltage drop with charging current, V/I, and not impedance, which ismore a measure of current collection.

Though not wishing to be bound by this theory, there are severalexplanations for the improvement in discharge rate capability. Asdiscussed previously, there are commonly known methods, techniques andexpedients to improve rate capability beyond alloy modification. Thesemay involve the attainment of very small particle size by grinding,i.e., to provide increased surface area, electrode pretreatment, i.e.,to provide the electrode surface oxide with enhanced porosity, andelectrode and powder coatings to provide a conductive, oxidationresistant coating.

Improvements in discharge rate through alloy modification avoids theseelaborate, costly, and time consuming methods, and provides significantand practically achieved improvement. First, discharge voltage may beincreased through changes to the metal-hydrogen bond or metal hydrideheat of formation. The modifier elements (Al, Mn, Mo, Cu, W, Fe, Co, andcombinations thereof) are not to be considered as "mixed in," butpresent in the particular alloy phases. For example in the compositionV₂₂ Ti₁₆ Zr i35Cr₇, there is a phase which is identified aspredominantly V-Cr. By adding the modifiers to this and the otherphases, essentially the hydride is destabilized, and according tothermodynamic principles, voltage is higher.

A second route for improved discharge rate capability relates to bulkdiffusion of hydrogen within the alloy. In one model for how thesemultiphase materials work, the argument is made for "storage" and"catalyst" phases. Essentially, the model considers that phases such asV-Cr store large quantities of hydrogen, but as individual phases mayhave very low discharge rate capability. Rather, in the multiphasealloy, this phase is in intimate contact with other phases, which alsostore hydrogen, but have much higher rate capability. One aspect of theinvention described herein is the modification of intra-phase grainboundaries. As viewed from a scanning electron microscope, the grainboundaries of the modified hydrogen storage materials of the inventionare "less distinct", i.e., more diffuse then the grain boundaries of theV-Ti-Zr-Ni-Cr alloy described in Venkatesan et al. It is believed thatthese grain boundaries may provide rapid diffusion of hydrogen fromstorage phases to catalyst phases, where the hydrogen reacts withhydroxyl ions for discharge.

A third route to improved discharge rate capability relates to activesurface area. It is possible through alloy modifications tosubstantially increase or decrease the amount of "cracking" of themetal. During charge/discharge cycling the metal hydride materialexpands and contracts as hydrogen is stored and released. This canprovide a volumetric expansion of the hydrogen storage alloy of up to 20percent. Metallurgically, some metallic alloys can not handle the stressof this massive expansion, and form cracks. For some applications, thisis a problem as the structural integrity of the electrode may beinadequate. However, with proper cell design, structural integrity canbe compensated, while preserving the high surface area that isadvantageous for high rate discharge. High surface area resulting fromalloy modification is a vast improvement over high surface area attainedby other methods, such as very fine powder grinding, as it avoids theelaborate processing steps associated therewith and provides "in situcreated surface area," i.e., surface area formed inside the cell. Thistype of surface area, which is associated with the modifiers describedand claimed herein is desirable as it avoids oxidation due toatmospheric exposure during fabrication, which can lead to difficultactivation (high pressure, low capacity, low rate capability, andexpensive electrical formation procedures) and corrosion products in thecell. The modifiers may be acting as embrittlement agents by decreasingthe metallurgical ductility of the host alloy. As part of the invention,it has been noted that some modified alloys are harder then the host V₂₂Ti₁₆ Zr 39Cr₇, supporting the proposition that ductility is probablydecreased, since usually hardness and ductility are inverselyproportional.

A fourth route to improved high rate discharge through alloymodifications relates to surface oxidation properties. As previouslynoted hereinabove, researchers have attempted to provide coatings topowder or electrodes in order to prevent or minimize oxidation in thehighly alkaline electrolyte. It should be noted that the metalhydroxide/electrolyte interface is the reaction site during cell chargeand discharge. Thus, the surface oxide must allow hydrogen to react withhydroxyl ions. Consequently, the oxide thickness, porosity,conductivity, and presence of catalyst are all important. The modifierelements may assist one or more of these features, although in this caseindividual modifier elements do not all function identically. Aluminum,for example, would be expected to oxidize and "leach out" from thesurface, probably assisting in providing porosity to the oxide, perhapsviewed as roughness quality. On the other hand, Mn, Mo, Cu, W, Fe, andCo might be reducing oxide thickness, and providing a more conductiveand/or catalytic component to the surface, and, while their oxides canin some cases corrode, probably function less in providing surfaceporosity then does aluminum.

Improved discharge rate through alloy modification may also involvelowering activation polarization of the metal hydride electrode. It isbelieved that the presence of Mn, Mo, Cu, W, Fe, Co, and Co-Mn-Alcombinations at the metal-electrolyte interface lower the voltage dropacross the electrochemical double layer. This may occur by lowering theenergy barrier of the charge-transfer step, essentially lowering theovervoltage of the charge transfer step. By catalysing thehydrogen/hydroxyl reaction, the activation of adsorbed surface speciesis easier. For example, oxides of Co may be promoting the reduction ofspecies like hydroxyl ion.

Another important route to improved discharge rate capability relates toimproved metal hydride electrode activation, especially in a sealedcell. Improved degree of activation raises the distinction between an"as fabricated" metal hydride electrode and an "activated" metal hydrideelectrode, especially as related to surface area and surface oxide. Forexample, the surface area of an "activated" metal hydride electrodemight increase by two or even three orders of magnitude during cyclingas compared to an "as fabricated" metal hydride electrode, while "asfabricated" surface oxides may be inappropriate for charge acceptance ordischarge. Surface area increase in a sealed cell is especiallydifficult, primarily because sealed cells use excess metal hydridecapacity for overcharge/discharge reactions, essentially underutilizingthe metal hydride electrode, i.e., lowering the metal hydride depth ofdischarge.

Improved activation using modified alloys may relate to easilyovercoming initial surface oxides (as in the case of Al), but also byquick and easy "desired surface area attainment" during initial cycling,especially in the sealed cell for a metal hydride electrode with a lowdepth of discharge. It is believed that Al, Mn, Mo, Cu, W, Fe, Co, andcombinations of Co, Mn, and Al all may function in this manner.

Another function of alloy modification is enhancement of low temperaturecapability, either by increasing capacity or by increasing dischargevoltage. Inherent low temperature limitations in electrochemicalapplications are commonly known. The most common explanation for poorlow temperature performance relates to the reaction:

    MH+OH.sup.- =M+H.sub.2 O+e.sup.-

where water is formed at the metal hydride surface, causing polarizationand lowered capacity. This explanation is certainly valid to somedegree, and is perhaps dominant based on polarization studies showingheavy concentration dependence. Other contributing factors may relate tothermodynamic and activation polarization components. Thermodynamiccontributions can be understood by referring to the "PCT Behavior" orequilibrium hydrogen pressure measurements as a function of hydrogencontent at a given temperature. In these measurements, lowering the testtemperature from +25° to -20° Celsius substantially lowers theequilibrium hydrogen pressure. This will be seen as a voltage drop inthe cell of perhaps 100 mV, or more. Activation polarization at lowtemperatures is perhaps not a large contributing factor, butnevertheless the catalytic properties of the metal hydride surface mayhave some temperature dependence.

Improvement in low temperature capability through alloy modification bythe addition of Al, Mn, W, Fe, Co, and particularly combinations of Co,Mn, and Al, may function by one or more of:

A decrease in concentration polarization due to water generation byincreased surface area.

A decrease in activation polarization by less temperature sensitivity ofcatalysis at reduced temperatures.

Less thermodynamic temperature sensitivity by alteration of the M-H bondwith particular phases and the alloy as a whole.

It is well known in electrochemistry that concentration polarizationproblems indicate mass transfer limitations of the reactants orproducts. Traditionally, methods of correction involve increasing theconcentration of a critical species, or increasing pathways at anelectrode. Stated simply, this means increasing porosity, pore size,and/or surface area. All of these methods will have a beneficial effectto some degree, but frequently are impractical for overall performancecharacteristics such as energy density, cycle life, etc. The method ofalloy modification does not have these limitations and shortcomings. Infact, the dramatic improvement for some alloys, as described in theExamples, was accomplished with standard concentrations and compositionsof electrolyte, and with standard electrode porosity and initial powdersize. These facts give support to the idea that the factors describedabove are critical and can be influenced.

Alloy modification improvements are believed to address all threefactors, namely concentration polarization, activation polarization, andthermodynamic properties. Essentially, concentration problems involvethe amount of water generated, which is completely dependent on thedischarge rate. However, the "water thickness" can be drasticallyaffected by the amount of surface area provided over what area the wateris generated. Of course, it is also important that pore size andporosity be sufficient to allow fast diffusion. Like high ratedischarge, surface area increase due to metallurgical modification ofthe alloy by Al, Mn, W, Fe, Co, and Co, Mn, Al combinations, would beexpected to assist low temperature performance. This, in fact, iscorrect, but the effects do not correlate completely. This supports thecontention that other factors related to alloy modification, such asthermodynamic or activation polarization phenomena, contribute to theoverall effect.

Cycle life as a particularly important parameter for a nickel hydridesecondary battery. Cycle life is defined as the number ofcharge/discharge cycles that a battery can be subjected to under a givenset of conditions to a defined cutoff point. The cutoff point is usuallya desired capacity expressed as a stated percentage of originalcapacity.

Many parameters relating to the metal hydride electrode can influenceoverall cycle life in a sealed cell with a Ni hydroxide positiveelectrode. For example, it is important that the negative electrodemaintain mechanical integrity upon repeated charge/discharge cycling.This is important because, as noted above, alloy modification frequentlyprovides higher surface area through a "cracking" phenomena, and the"cracking" might be expected to compromise structural integrity.

Another important parameter is generally referred to as "oxidation."Generally, oxidation can adversely affect cycle life in many ways.Build-up of oxide at the metal hydride electrode can reduce chargingefficiency; raising internal pressure levels possibly to the degree ofvent release, resulting in a loss of electrolyte, and thereby in animpaired state of electrode charge. Oxidation also causes loweredelectrode capacity by effectively insulating portions of powder in theelectrode, thus rendering that powder electrochemically inactive.Oxidation can also affect charge balance in the cell. Formation of metaloxides from water or hydroxyl ion can decrease electrolyte amount,liberate hydrogen 9as, or decrease electrolyte concentration. Buildup ofsurface oxide substantially increases the polarization of the metalhydride electrode, causing an undesirable decrease in voltage ondischarge, and an increase in charging voltage. Some of the metal oxideswhich form upon reaction with the electrolyte or during oxygenrecombination are soluble or can form precipitates. This is undesirable.Vanadium, for example, has been proven to be easily soluble, and able toform redox shuttle mechanisms, thereby increasing self discharge.

The prior art is silent as to other oxidation related problems as well,for example, oxidation problems related to the detrimental effects onthe positive electrode and on overall cell operation. Oxides of titaniumand zirconium have also been observed to impair cell operation. Withvery low solubility, it would be expected that TiO₂ and ZrO₂ orderivatives thereof would simply buildup at the metal hydride surface.Though undesirable for the reasons states above, the less obvious facthas been the observance of TiO₂ and ZrO₂ at the nickel hydroxidepositive electrode and the separator.

Though not wishing to be bound by this theory, it is believed that theseoxides have been precipitated, possibly causing two problems. The firstproblem is that the oxides have a high surface area. It is believed thatthese high surface area oxides at the negative and positive electrodesand at the separator retain electrolyte by capillary action. For asealed cell, this is undesirable since, by definition, there is a finiteelectrolyte supply, and, ultimately, electrolyte redistribution is adominant failure mode. Normally, electrolyte redistribution occursthrough inevitable expansion of both electrodes. By having a sidereaction which can steal electrolyte, the problem is accelerated. Thesecond is that the nickel hydroxide positive electrode dramaticallyloses charging efficiency upon extended charge/discharge cycling. It isbelieved that TiO₂ and ZrO₂ precipitates, which are not only at theouter electrode surface, but have been found deep in the nickelhydroxide electrode interior, are promoting premature oxygen evolution.This effectively reduces cell capacity. It is believed that TiO₂ andZrO₂ catalyze the oxygen evolution ostensibly by lowering the oxygenovervoltage on charge.

Alloy modification of the V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇ type alloy hassubstantially improved cycle life of sealed cells incorporating themodified alloys as compared to sealed cells with unmodified V₂₂ Ti₁₆Zr₁₆ Ni₃₉ Cr₇ type alloy negative electrodes. While even the standardV-Ti-Zr-Ni-Cr material has demonstrated acceptable cycle life, by alloymodification the cycle life has been extended, while maintaining goodcharging efficiency. This has been verified under aggressive testconditions

Before discussing the very important improvements of alloy modificationrelated to oxidation, it should be noted that mechanical stability ofthe metal hydride electrode has been improved. This result is surprisingsince alloy modification has improved activation, high rate discharge,and low temperature performance, at least in part due to higher attainedsurface area. Yet inspection of highly cycled cells and half cellnegative electrodes with modified alloy has shown improved mechanicalintegrity. In flooded half-cell testing, which emphasizes mechanicalintegrity over oxidation resistance due to the high depth of discharge,lack of physical restraint, and no oxygen recombination, it is common toobserve material "falling off of the substrate" during cycling. In thisregard the alloy V₂₀.6 Ti₁₅ Zr₁₅ Ni₃₀ Cr₆.6 Co₆.6 Mn₃.6 Al₂.7 has shownbetter particle to particle bonding and better adherence to thesubstrate than the standard V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇ type material of theprior art. In sealed cell testing the cobalt modified alloy, V₂₂ Ti₁₆Zr₁₆ Ni₃₂ Cr₇ Co₇, has been inspected after 250 cycles and found to haveremarkable integrity, i.e., substantially better then the prior art V₂₂Ti₁₆ Zr₁₆ Ni₃₉ Cr₇ Other alloy compositions having good cycle life, forexample, those alloys modified by Mn, Cu, Fe, Co, and other Co-Mn-Al,may also be functioning through improved structural integrity.

Though not wishing to be bound by this theory, it is believed that thealloy modifiers may be quickly achieving a steady state high surfacearea. That is, the alloys may be brittle enough that during initialcycling large amounts of new surfaces are formed but the new surfacearea quickly reaches a limiting value upon extended cycling. Frommetallurgical considerations, it is possible this relates to a moreoptimized stress-strain relationship, or toughness providing theelectrochemically desirable properties of:

High surface area formed in situ.

Fast activation (surfaces formed quickly)

Reduced formation of new surfaces area during extended cyclingthereafter.

The alloy modifications are also considered to address oxidation andcorrosion of the metal hydride alloy during cycling. One measure of theimprovement is improved corrosion resistance for the Co modified alloy,V₂₀.6 Ti₁₅ Zr₁₅ Ni₃₀ Cr₆.6 Co₆.6 Mn₃.6 Al₂.7, as compared to theunmodified alloy, V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇. This is illustrated withparticularity in the Examples below.

Many of the modifiers exhibit particularly improved charging efficiencycompared to unmodified alloys. More specifically, Mn and Cu showimproved charging efficiency. Fe, and Co-Mn-Al combinations, and mostparticularly Co show even greater improvements in charging efficiency.This is shown and described in the Examples hereinbelow.

Though not wishing to be bound by this theory, the modifications appearto be improving cycle life by improved oxidation resistance. Forexample, while cobalt does oxidize and is soluble, the cobalt oxide maybe inhibiting further oxidation of the other elements. Another aspect ofthe invention is improved oxygen recombination. Previously, it wasobserved that oxygen gas generated at the nickel hydroxide positiveelectrode recombined at the surface of the metal hydride electrode.Oxygen recombination is an especially aggressive oxidizer of itsenvironment, even compared to the alkaline electrolyte. It is possiblethat the modifier elements, particularly Mn and Fe, and mostparticularly Co, either alone or in combination with, e.g., one or bothof Mn and Al, act to catalyze the oxygen reduction, thereby avoiding orreducing the oxidation of the surrounding elements in the metal hydridealloy. It is believed that this function of the modified alloy reducesor even eliminates the formation and build-up of detrimental surfaceoxide, thereby providing a thinner and more stable surface.

Another aspect of the improved oxidation resistance by alloymodification again relates to improved corrosion resistance. It waspreviously discussed hereinabove that TiO₂ and ZrO₂ can affect nickelhydroxide oxygen evolution and that oxides of vanadium are quitesoluble, providing excessive self discharge. The modified alloyseliminate these problems in at least two ways. Again, while not wishingto be bound by this theory, it is believed that levels of TiO₂, ZrO₂,and V₂ O₅ are significantly reduced by simply inhibiting their formationat the metal hydride surface, thereby preventing corrosion and migrationof the species. Second, and quite surprisingly, we have observed thatmodifiers are precipitated at the Ni hydroxide positive electrode. Thesurprising aspect of finding modifiers precipitated at the Ni electrodeis the fact that the modifiers function by inhibiting oxidation andcorrosion. Yet, the oxidation/corrosion inhibiting specified, i.e.,cobalt, is found precipitated at the nickel electrode as cobalt oxide.

This finding suggests still other aspects of the oxidation-corrosionbenefits of the modified alloys of the invention disclosed herein.First, it is possible that the modifier dissolves from the negativeelectrode in one oxidation state and precipitates at the positiveelectrode in another oxidation state. For example, Co⁺² is readilysoluble while Co⁺³ readily precipitates. It is possible the cobaltprecipitate inhibits the reduced levels of TiO₂, ZrO₂, and V₂ O₅ fromreaching the nickel hydroxide surface, thereby avoiding their poisoningeffect of promoting premature oxygen evolution. Second, it is possiblethe detrimental TiO₂, and ZrO₂ reduction in oxygen overvoltage iscompensated or eliminated by the presence of modifier oxides,particularly cobalt oxide. Cobalt is commonly an additive to the nickelhydroxide electrode as cobalt hydroxide, to improve oxygen evolution,activation, and capacity utilization. It is possible that cobalt oxideadded to the positive electrode by precipitation from the negativeelectrode is a different, and particularly successful method ofincreasing overvoltage, thereby postponing oxygen evolution andproviding good charging efficiency, capacity, and cycle life.

The electrode materials of the invention are a complex multiphasepolycrystalline structure of the active electrode materials, i.e., morecomplex than those described in the aforementioned U.S. Pat. No.4,728,586 of Srini Venkatesan, Benjamin Reichman, and Michael A.Fetcenko for ENHANCED CHARGE RETENTION ELECTROCHEMICAL HYDROGEN STORAGEALLOYS AND AN ENHANCED CHARGE RETENTION ELECTROCHEMICAL CELL, thedisclosure of which was incorporated herein by reference. The materialsof Venkatesan et al. include a grain phase which is an intermetalliccompound of vanadium, titanium, zirconium, and nickel, with dissolvedchromium. The grain phase reversibly stores hydrogen and also hassuitable catalytic activity to promote rapid hydrogen oxidation. Thecomposition of this grain phase is about 19:16:19:42:4 as an atomicratio of vanadium:titanium zirconium:nickel:chromium.

Between the grain phases of the polycrystalline structure of Venkatesanet al is a primary intergranular phase which is a solid solution ofvanadium, chromium, titanium, and nickel. The composition of thisintergranular phase is about 65:27:3:5 as an atomic ratio ofvanadium:chromium:titanium:nickel. This intergranular phase is believedto be a hydrogen storing phase, with limited catalytic activity forhydrogen oxidation.

Several other phases may be present along with the above mentioned twodominant phases. These phases are dependent on the fabricationconditions of the alloy and electrode. Although not wishing to be boundby theory, it is not believed that the degree of these alternate phasesplay a critical role in the enhanced properties of the compositionallyand microstructurally modified electrodes of the invention.

The phase compositions identified above are for one particularcomposition, which is disclosed to be a preferred composition ofVenkatesan et al. It should be understood that the specific phasecompositions for the entire family of

(Ti₀.33-x Zr_(x) V₀.67-y Ni_(y))_(1-z) Cr_(z)

where x, y, and z have been previously specified, are variable anddependent on the individual composition. The value of z is such as toallow the Cr to be up to 20 atomic percent of the alloy.

Venkatesan et al discloses that with chromium as a modifier to theV-Ti-Zr-Ni family, the chromium should be present in the primary grainphase on the order of from about 0 to 10 atomic percent, and preferablyabout 4 atomic percent. Venkatesan et al further discloses that thechromium should be present in the primary intergranular phase on theorder of 0 to 35 atomic percent and preferably about 27 atomic percent.Alloys as described by Venkatesan et al are particularly susceptible tofurther improvements in charge retention by the provision of a highlyconcentrated electrolyte as described herein.

Some of the compositionally and microstructurally modified electrodematerials of the instant invention have the following characteristics:

1. (V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇)₉₅ W₅, modified by the addition of a smallamount of tungsten, exhibits at least five phases, having the followingatomic ratios for the respective Zr:Ti:Ni:V:W; V:Ti:Zr:Ni:Cr:W;Ti:Zr:Ni:V:W; and V:Cr:Ti:Zr:Ni:W phases with the compositions89.5:5.9:1.1:2.8:Tr; 21.9:17.2:17.8:41.9:0.9:0.3;30.9:15.4:3.8:49.8:Tr:0.6; and 79.1:5.9:4.1:1.8:2.2; also present is aV₆₄.6 Ti₂.8 Zr₄.3 Ni₃.9 Cr₄.3 W₂₀.2 phase; the addition of a smallamount of tungsten modifier results in the properties described above,and W going preferentially in the "V-Cr" phase.

2. V₂₀.6 Ti₁₅ Zr₁₅ Ni₃₀ Cr₆.6 Co₆.6 Mn₃.6 Al₂.7. This alloy has at leastfour phases, with the SEM/EDS compositions: Zr:Ti:Ni:V:Co:Mn:Al;V:Ti:Zr:Ni:Cr:Co:Mn:Al; Ti:Zr:Ni:V:Co:Mn:Al; and V:Cr:Ti:Zr:Ni:Co:Mn:Al;phases with the compositions 92.3:1.3:5.4:0.7:0.3;19.6:14.8:17.0:28.7:6.8:8.0:4.0:1.2; 32.3:42.5:7.2:6.2:1.0:6.3:1.5:3.2;and 58.4:26.4:3.3:1.3:3.0:3.8:0.0 phases;

The active negative electrodes of the invention disclosed herein can beutilized in many types of cells having a metal hydride, hydrogen storagenegative electrode and batteries. Referring now to FIGS. 1 and 2,various electrochemical cell embodiments utilizing the negativeelectrode of the invention are set forth. In FIG. 1, a flat cell 10 isillustrated that includes a substantially flat plate negative electrode12 in accordance with the invention. Electrode 12 includes a currentcollector 14 that is in electrical contact with the active material ofelectrode 12 and a tab 16. Collector 14 and tab 16 may be made ofsuitably conductive metals such as nickel. Flat cell 10 includes apositive electrode or counter electrode 18 which is substantially flatand aligned to be in operative contact with negative electrode 12. Aseparator 20 is disposed between counter electrode 18 and negativeelectrode 12.

A second negative electrode 22 may be spaced in operative contact withthe counter electrode 18 on the side of counter electrode 18 oppositenegative electrode 12. Negative electrode 22 is similar to electrode 12and includes a current collector 24 which is in electrical contact withthe active material of electrode 22 and tab 26. A second separator 28 isdisposed between negative electrode 22 and the counter electrode 18.

Cell 10 depicted in FIG. 1 may be sealed in a suitable material, such asa plastic container 30, which does not deteriorate in contact with theelectrolyte used and allows venting of cell 10 should it gas beyond apredetermined limit during operation. A 30 weight percent aqueoussolution of potassium hydroxide is a preferred electrolyte. First andsecond tabs 16 and 35, 26 are electrically connected to a first set ofleads 32 that extends outside of the cell plastic 30. Likewise, a secondlead 34 electrically connects to counter electrode 18 and extendsoutside of plastic container 30.

FIG. 2 illustrates a commercially preferred jelly-roll cell 36 that ismade by spirally winding a flat cell about an axis 38. Jelly-roll cell36 includes an electrical contact tab 40, a negative electrode 42,separator 44 and a positive electrode 46. Jelly-roll cell 36 may beplaced in a can or other suitable container (not shown) that contactstab 40 connected to negative electrode 42. Separator 44 is positionedbetween the negative electrode 42 and the positive electrode 46.

The following examples are illustrative of the method of the invention.

EXAMPLES Example I

A series of V-Ti-Zr-Ni-Cr-M'-M"-M^(iii) -M^(iv) electrochemical hydrogenstorage alloys were cast, and fabricated into negative electrodes fortesting in sealed, alkaline cells.

Alloys having the compositions shown in Table 1-1 were prepared byweighing and mixing powders of the individual metals into a graphitecrucible. The crucible and its contents were placed in a vacuum furnace.The furnace was taken down to a vacuum, and then pressurized with aninert gas. The crucible contents were then melted by high frequencyinduction melting while under the inert gas atmosphere. The melting wascarried out at a temperature of about 1500° C. for a long enough time toobtain a uniform melt. The melt was then solidified to obtain an ingotof hydrogen storage alloy.

The ingot of hydrogen storage alloy was then reduced in size. This was amulti-step process. The first step was a hydride/dehydride process,substantially as described in the commonly assigned, copending U.S.application Ser. No. 07/247,569, filed Sept. 22, 1988 of Michael A.Fetcenko, Thomas Kaatz, Steven P. Sumner, and Joseph A. LaRocca, forHYDRIDE REACTOR APPARATUS FOR HYDROGEN COMMINUTION OF METAL HYDRIDEHYDROGEN STORAGE ALLOY MATERIAL, and incorporated herein by reference.In this first step the hydrogen storage alloy ingot was reduced in sizeto -100 mesh.

The -100 mesh hydrogen storage alloy material obtained from thehydride/dehydride process was further reduced in size by impact milling.In the high speed impact milling process used to prepare the samples forthe Examples described herein, the -100 mesh hydrogen storage alloyparticles were tangentially and radially accelerated against an impactblock. This was substantially as described in our commonly assigned,copending, U.S. application Ser. No. 07/308,289 filed Feb. 9, 1989, inthe names of Merle Wolff, Mark A. Nuss, Michael A. Fetcenko, Andrea A.Lijoi, Steven P. Sumner, Joseph LaRocca, and Thomas Kaatz, for IMPROVEDMETHOD FOR THE CONTINUOUS FABRICATION OF COMMINUTED HYDROGEN STORAGEALLOY NEGATIVE ELECTRODE MATERIAL, and incorporated herein by reference.

A fraction of hydrogen storage alloy material was recovered from theimpact milling process. This fraction was minus 200 mesh, with a massaverage particle size of about 400 mesh (38 micron).

The minus 200 mesh fraction of hydrogen storage alloy material powderwas then bonded to a nickel screen current collector. Bonding wascarried out by disposing a layer of the hydrogen storage alloy powderonto the current collector, and compacting the powder and currentcollector. Compacting was carried out under an inert atmosphere, withtwo compaction steps, each at a pressure of about 16 tons per squareinch of current carrier. Thereafter the current collector and powderwere sintered in an atmosphere of 2 atomic percent H₂, balance argon.

Samples of the resulting negative electrodes were then tested forelectrode capacity in beaker cells with 30 weight percent KOHelectrolytes. Electrodes of about 16 grams were tested with excesspositive electrode capacity, and a Hg/HgO reference electrode. Theelectrodes were charged at 500 mA for 15 hours, and subsequentlydischarged at 500 mA to a voltage of -0.700 volt versus the Hg/HgOreference electrode. The capacity of each of the negative electrodes wasmeasured at a 50 mA/g. The measured capacities are shown in Table I-2.

                  TABLE I-2                                                       ______________________________________                                        ELECTRICAL PROPERTIES AS                                                      A FUNCTION OF COMPOSITION                                                                         CAPACITY                                                                      milliAmpere                                               COMPOSITION         hours per gram                                            ______________________________________                                        1.    (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Al.sub.5                               342                                                   2.    (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Mn.sub.5                               355                                                   3.    (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Cu.sub.5                               333                                                   4.    (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 W.sub.5                                320                                                   5.    (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Fe.sub.5                               355                                                   6.    (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Co.sub.5                               349                                                   7.    V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7                                                 320                                                         (Control)                                                               8.    V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.32 Cr.sub.7 Co.sub.7                                        349                                                   9.    V.sub.20.6 Ti.sub.15 Zr.sub.15 Ni.sub.30 Cr.sub.6.6                                             320                                                         Co.sub.6.6 Mn.sub.3.6 Al.sub.2.7                                        10.   V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.27.8 Cr.sub.7                                               320                                                         Co.sub.5.9 Mn.sub.3.1 Al.sub.2.2                                        ______________________________________                                    

                  TABLE I-1                                                       ______________________________________                                        COMPOSITIONS                                                                  ______________________________________                                        1.       (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95                      Al.sub.5                                                             2.       (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95                      Mn.sub.5                                                             3.       (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95                      Cu.sub.5                                                             4.       (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95                      W.sub.5                                                              5.       (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95                      Fe.sub.5                                                             6.       (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95                      Co.sub.5                                                             7.       V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7                               (Control)                                                            8.       V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.32 Cr.sub.7 Co.sub.7             9.       V.sub.20.6 Ti.sub.15 Zr.sub.15 Ni.sub.30 Cr.sub.6.6 Co.sub.6.6                Mn.sub.3.6 Al.sub.2.7                                                10.      V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.27.8 Cr.sub.7 Co.sub.5.9                  Mn.sub.3.1 Al.sub.2.2                                                ______________________________________                                    

This Example particularly shows the effect of the modifiers Al, Mn, Cu,W, Fe, and Co, and the combination of Co, Mn, and Al on the capacity.Also to be noted is that the particular substitution is critical. Forexample in samples 1 through 6 the modifier is partially substitutingfor the V-Ti-Zr-Ni-Cr, while in samples 8 through 10 the modifier ispartially substituting for the Ni only. Sample 7 is a V-Ti-Zr-Ni-Crcontrol.

Example II

In this example sealed cells were fabricated to measure the effects ofspecific modifiers, modifier substitutions, and modifier combinations onmidpoint cell voltage.

Negative electrode materials were prepared as described in Example I,above. The resulting negative electrodes were trimmed to size, andwound, with polyimide separators and Ni(OH)₂ positive electrodes, toform "jelly rolls". These jelly rolls were then placed in "C" size cellcans, a 30 weight percent KOH electrolyte solution was added to eachcell can, and the cells were sealed to form starved, sealed "C" cells.

Each of the cells were tested under identical conditions, and undervarying discharge rates. The midpoint cell voltages were recorded, andare reported in Table II-1.

                  TABLE II-1                                                      ______________________________________                                        ELECTRICAL PROPERTIES AS                                                      FUNCTION OF COMPOSITION                                                                      MIDPOINT VOLTAGE                                                              700 mA  2 Amp   4 Amp                                          ______________________________________                                        (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Al.sub.5                              1.20 V    1.18 V  1.14 V                                     (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Mn.sub.5                              1.22 V    1.19 V  1.15 V                                     (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Mo.sub.5                              1.21 V    1.18 V  1.14 V                                     (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Cu.sub.5                              1.22 V    1.17 V  1.14 V                                     (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 W.sub.5                               1.22 V    1.19 V  1.14 V                                     (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Fe.sub.5                              1.23 V    1.18 V  1.14 V                                     (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Co.sub.5                              1.23 V    1.20 V  1.16 V                                     V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7                                                1.22 V    1.17 V  1.13 V                                     (Control)                                                                     V.sub.33 Ti.sub.17 Zr.sub.17 Ni.sub.33                                                         1.16 V    1.15 V  1.10 V                                     V.sub.25 Ti.sub.17 Zr.sub.17 Ni.sub.42                                                         1.23 V    1.19 V  1.14 V                                     V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.32 Cr.sub.7 Co.sub.7                                       1.23 V    1.19 V  1.14 V                                     V.sub.20.6 Ti.sub.15 Zr.sub.15 Ni.sub.30 Cr.sub.6.6                                            1.23 V    1.21 V  1.17 V                                     Co.sub.6.6 Mn.sub.3.6 Al.sub.2.7                                              V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.27.8 Cr.sub.7                                              1.22 V    1.19 V  1.14 V                                     Co.sub.5.9 Mn.sub.3.1 Al.sub.2.2                                              ______________________________________                                    

EXAMPLE III

The cells of Example 11 were also tested for capacity and the resultsshown in Table 111-1 were obtained.

Example IV

A series of tests were conducted under half cell conditions to determinethe internal resistances of the electrodes. Negative electrode samples,each with approximately 16 grams of active material and of the typedescribed in Example I, were tested. The tests were carried out withexcess electrolyte, excess capacity positive electrodes, and with aHg/HgO reference electrode to measure the half cell voltage.

In the tests the negative electrodes were cycled through twocharge/discharge cycles, with charging at 500 mA to 150% of electrodecapacity. The electrodes were measured for discharge polarization on thethird cycle.

The discharge was done under the repetitive pulse conditions shown inTable IV-1, hereinbelow, with the metal hydride electrode versus theHg/HgO electrode being continuously monitored. The polarization valuesare listed in Table IV-2, hereinbelow. It should be noted that themagnitude of the internal resistance is highly dependent on testconditions, and that comparative results

                  TABLE III-1                                                     ______________________________________                                        ELECTRICAL PROPERTIES AS                                                      FUNCTION OF COMPOSITION                                                                    ELECTRICAL CAPACITY                                                           700 mA  2 Amp     4 Amp                                          ______________________________________                                        (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Al.sub.5                            3.44 AH   3.28 AH   3.12 AH                                    (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Mn.sub.5                            3.47 AH   3.33 AH   3.15 AH                                    (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Mo.sub.5                            3.51 AH   3.36 AH   3.21 AH                                    (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Cu.sub.5                            3.59 AH   3.46 AH   3.30 AH                                    (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 W.sub.5                             3.59 AH   3.44 AH   3.33 AH                                    (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Fe.sub.5                            3.61 AH   3.47 AH   3.37 AH                                    (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Co.sub.5                            3.71 AH   3.57 AH   3.52 AH                                    V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7                                              3.64 AH   3.44 AH   3.40 AH                                    (Control)                                                                     V.sub.33 Ti.sub.17 Zr.sub.17 Ni.sub.33                                                       3.46 AH   2.97 AH   2.54 AH                                    V.sub.25 Ti.sub.17 Zr.sub.17 Ni.sub.42                                                       3.70 AH   3.55 AH   3.35 AH                                    V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.32 Cr.sub.7 Co.sub.7                                     3.68 AH   3.56 AH   3.47 AH                                    V.sub.20.6 Ti.sub.15 Zr.sub.15 Ni.sub.30 Cr.sub.6.6                                          3.66 AH   3.58 AH   3.37 AH                                    Co.sub.6.6 Mn.sub.3.6 Al.sub.2.7                                              V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.27.8 Cr.sub.7                                            3.70 AH   3.48 AH   3.37 AH                                    Co.sub.5.9 Mn.sub.3.1 Al.sub.2.2                                              ______________________________________                                    

                  TABLE IV-1                                                      ______________________________________                                        PULSE CONDITIONS                                                              FOR DETERMINING                                                               INTERNAL RESISTANCE                                                           TIME                CURRENT                                                   Seconds             Amperes                                                   ______________________________________                                        60 seconds           0 Amperes                                                60 seconds          700 MA                                                    60 seconds           2 Amperes                                                60 seconds           5 Amperes                                                ______________________________________                                    

                  TABLE IV-2                                                      ______________________________________                                        ELECTRICAL PROPERTIES AS                                                      FUNCTION OF COMPOSITION                                                                      INTERNAL RESISTANCE                                                           (OHMS)                                                         ______________________________________                                        (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Al.sub.5                              0.52                                                         (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Mn.sub.5                              0.49                                                         (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Mo.sub.5                              0.42                                                         (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Cu.sub.5                              0.50                                                         (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 W.sub.5                               0.54                                                         (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Fe.sub.5                              0.31                                                         (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95 Co.sub.5                              0.48                                                         V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7                                                0.51                                                         (Control)                                                                     V.sub.33 Ti.sub.17 Zr.sub.17 Ni.sub.33                                                         0.52                                                         V.sub.25 Ti.sub.17 Zr.sub.17 Ni.sub.42                                                         0.30                                                         V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.32 Cr.sub.7 Co.sub.7                                       0.48                                                         V.sub.20.6 Ti.sub.15 Zr.sub.15 Ni.sub.30 Cr.sub.6.6                                            0.42                                                         Co.sub.6.6 Mn.sub.3.6 Al.sub.2.7                                              V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.27.8 Cr.sub.7                                              0.48                                                         Co.sub.5.9 Mn.sub.3.1 Al.sub.2.2                                              ______________________________________                                    

are only valid if the tests are carried out under identical conditions.In the tests reported hereinabove, the tests were carried out underidentical conditions.

To be particularly noted is that what appear to be slight changes incompositions of the alloys can actually cause very significantdifferences in parameters.

Example V

Cells of the type utilized in Examples 11 and 111, above, were wereutilized to determine the cold temperature characteristics as a functionof the negative electrode composition. In each test the cells werecharged at room temperature, and at a charging current of 350 mA, forfifteen hours. The cells were then placed in a cold temperature cabinet,at a temperature of minus 20° C. for six hours on open circuit. Thecells were then discharged at minus 20° C. at a 1.75 Amp dischargecurrent. The capacity to a 0.85 Volt cutoff, and the midpoint voltageare reported in Tables V-1, and V-2, respectively.

Example VI

Two electrode samples of the type described in Example I, hereinabove,underwent life cycle testing. The electrodes were formed of V₂₂ Ti₁₆Zr₁₆ Ni₃₉ Cr₇ and V₂₀.6 Ti₁₅ Zr₁₅ Ni₃₀ Cr₆.6 Co₆.6 Mn₃.6 Al₂.7.

The two negative electrode samples, each with approximately 16 grams ofactive material and of the type described in Example I, were tested. Thetests were carried out with excess electrolyte and excess capacitypositive electrodes, and with a Hg/HgO reference electrode tocontinuously measure and record the half cell voltage.

In the tests the negative electrodes were cycled through thecharge/discharge cycles, with charging at 500 mA to 150% of electrodecapacity. Discharge was also at 500 mA to a cutoff voltage of minus 0.7Volts versus the Hg/HgO reference electrode.

The results are reported in FIG. 3.

Example VII

Sealed cells of the type described in Examples II and 111, hereinaboveunderwent life cycle testing. During each cycle the cells were chargedat a charge current of 1.8 Amperes to a temperature cutoff, and thendischarged at a discharge rate of 2.0 Amperes to a cutoff voltage of 1.0volts. This test mode is especially agressive. Even with compositionsshowing capacity loss, the addition of overcharge causes capacity tosignificantly increase. Thus, this example illustrates chargingefficiency under cycle testing and is useful in the comparison ofcomposition effects.

The results are shown in FIGS. 4-1 through 4-8. The Figures arecorrelated with compositions in Table VII-1 below.

                  TABLE VI-1                                                      ______________________________________                                        CORRELATION OF FIGURE NUMBERS                                                 WITH COMPOSITIONS                                                             FIG.          Composition                                                     ______________________________________                                        4-1           V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7 (Control)       4-2           (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95                      Mn.sub.5                                                        4-3           (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95                      Cu.sub.5                                                        4-4           (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95                      Fe.sub.5                                                        4-5           (V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7).sub.95                      Co.sub.5                                                        4-6           V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.32 Cr.sub.7 Co.sub.7        4-7           V.sub.20.6 Ti.sub.15 Zr.sub.15 Ni.sub.30 Cr.sub.6.6                           Co.sub.6.6 Mn.sub.3.6 Al.sub.2.7                                4-8           V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.27.8 Cr.sub.7                             Co.sub.5.9 Mn.sub.3.1 Al.sub.2.2                                ______________________________________                                    

Example VIII

Certain modifiers affect the compared to electrodes of standard materialcomposition.

The cells which had been electrochemically cycled and tested for variouselectrochemical parameters were analyzed. One cell had a negativematerial composition of V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇ and was measured to havea low cycle life. The other cells had negative electrode materialcompositions that were modified according to the invention. Thesecompositions were: V₂₂ Ti₁₆ Zr₁₆ Ni₃₂ Cr₇ Co₇, V₂₀.6 Ti₁₅ Zr₁₅ Ni₃₀Cr₆.6 Co₆.6 Mn₃.1 Al₁₂.7, and V₂₂ Ti₁₆ Zr₁₆ Ni₂₇.8 Cr₇ Co₅.9 Mn₃.1Al₂.2. The cells with the modified composition negative electrodes wereall measured to have a high cycle life.

The cells were dismantled and analyzed for negative electrode surfacearea. This involved dismantling the cell in an Argon atmosphere. Thenegative electrodes then underwent Soxhlet extraction to remove thepotassium hydroxide electrolyte. The electrodes were then dried at about60° C. for a period of about 24 hours under an Argon environment. About1 to 2 grams from each dried electrode was used for surface areameasurement.

Surface area was determined by the well known gas absorption surfacearea measurement (BET) technique. The electrode segments were placed ina bulk sample cell and outgassed under a nitrogen purge at a temperatureof 250° to 300° C. The sample cell was then immersed in liquid nitrogenunder an atmosphere of 0.3 mole fraction nitrogen in balance Helium. Theamount of nitrogen absorbed is proportional to the sample surface areaand is measured using a Model Q5-9 Quantasorb™ surface area analyzer,manufactured by Quantachrome.

BET surface areas presented in Table VIII-1 are expressed as area insquare meters per gram of active material and are alternately expressedas roughness factor. The roughness factor is dimensionless, and is thetotal sample surface area divided by the outside or geometric surfacearea. To be noted is that the material with a poor cycle life had a lowBET surface area, and slowly attained a higher surface area, while thematerials with high cycle lives attained high BET surface areas afteronly a few cycles, e.g., six cycles.

                  TABLE VIII-1                                                    ______________________________________                                        SURFACE AREA                                                                                   Roughness Surface                                            Composition      Factor    Area (M.sup.2 /g)                                  ______________________________________                                        V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.39 Cr.sub.7                                                Control                                                      Cycle 5           3,300     5.8                                               Cycle 170        18,000    29.8                                               V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.32 Cr.sub.7 Co.sub.7                      Cycle 6          12,500    22.3                                               Cycle 250        13,200    24.1                                               V.sub.20.6 Ti.sub.15 Zr.sub.15 Ni.sub.30 Cr.sub.6.6                           Co.sub.6.6 Mn.sub.3.6 Al.sub.2.7                                              Cycle 6          12,500    22.3                                               V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.27.8 Cr.sub.7                             Co.sub.5.9 Mn.sub.3.1 Al.sub.2.2                                              Cycle 6          11,500    25.0                                               ______________________________________                                    

Example IX

The relative corrosion rates of V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇ (control) andV₂₀.6 Ti₁₅ Zr₁₅ Ni₃₀ Cr₆.6 Co₆.6 Mn₃.6 Al₂.7 (modified according to theinvention) were measured. Negative electrodes were prepared from eachalloy as described in Example 1. The electrodes, with about 16 gramseach of active material, corresponding to C size cells, were placed intoabout 100 ml of electrolyte.

Both the electrolyte concentration and the electrolyte temperature werecontrolled. Electrolyte samples were periodically removed and analyzedfor vanadium by atomic absorption analysis. Vanadium was selected as thetracer element because the vanadium level in the electrolyte isconsidered an overall measure of the corrosion properties of the alloy.This is because the vanadium is easily soluble in the electrolyte. Theresults were then normalized to correspond to an actual C cell having anelectrolyte level of about 6.5 ml.

FIGS. 5-1 through 5-3 show corrosion data for each alloy as a functionof time in 30% KOH at 60o C (FIGURE 5-1), 45% KOH at 200 C (FIG. 5-2),and 30% KOH at 20° C. (FIG. 5-3). In each case "CR07" corresponds to thecontrol material of the prior art, V₂₂ Ti₁₆ Zr₁₆ Ni₃₉ Cr₇ and "MF-16"corresponds to the modified material of the invention, V₂₀.6 Ti₁₅ Zr₁₅Ni₃₀ Cr₆.6 Co₆.6 Mn₃.6 Al₂.7.

It can be seen that under all conditions the standard alloy, "CR07", hassignificantly higher corrosion than the modified "MF-16" alloy.

While the invention has been described with respect to certain preferredexemplification and embodiment, it is not intended to limit the scope ofthe invention thereby, but solely by the claims appended hereto.

I claim:
 1. A V-Ti-Zr-Ni-Cr electrochemical hydrogen storage alloy inwhich the V, Ti, Zr, Ni and Cr are individually or collectivelypartially replaced by one or more modifiers, and the alloy has thecomposition:

    (V.sub.y'-y Ni.sub.y Ti.sub.x'-x Zr.sub.x Cr.sub.z).sub.a Co.sub.b Mn.sub.c Al.sub.d

where x' is between 1.8 and 2.2, x is between 0 and 1.5, y' is between3.6 and 4.4, y is between 0.6 and 3.5, z is between 0.00 and 1.44, adesignates that the V-Ni-Ti-Zr-Cr component, (V_(y'-y) Ni_(y) Ti_(x'-x)Zr_(x) Cr_(z)), as a group, is at least 70 atomic percent of the alloy,each of b, c, and d is from 0 to 20 atomic percent of the alloy, the sumof c+d is a positive number and the sum of b+c+d is an effective amountof modifiers up to 30 atomic percent of the alloy.
 2. The V-Ti-Zr-Ni-Crelectrochemical hydrogen storage alloy of claim 1 wherein the Comodifier partially replaces one or ore of V and Ni, and partiallyreplaces V-Ti-Zr-Ni-Cr.
 3. The V-Ti-Zr-Ni-Cr electrochemical hydrogenstorage alloy of claim 1 wherein the Mn and Al partially replaceV-Ti-Zr-Ni-Cr.
 4. The V-Ti-Zr-Ni-Cr electrochemical hydrogen storagealloy of claim 3 having the composition within the homogeneity range of

    V.sub.20.6 Ti.sub.15 Zr.sub.15 Ni.sub.30 Dr.sub.6.6 Co.sub.6.6 Mn.sub.3.6 Al.sub.2.7.


5. The V-Ti-Zr-Ni-Cr electrochemical hydrogen storage alloy of claim 4wherein the alloy is a multiphase alloy and individual phases of thealloy have compositions within the homogeneity ranges of:(i)Zr:Ti:Ni:V:Co:Mn:Al=92.3:1.3:5.4:0.7:0.3; (ii)V:Ti:Zr:Ni:Cr:Co:Mn:Al=19.6:14.8:17.0:28.7:6.8:8.0:4.0:1.2; (iii)Ti:Zr:Ni:V:Co:Mn:Al=32.3:42.5:7.2:6.2:1.0:6.3:1.5:3.2; and (iv)V:Cr:Ti:Zr:Ni:Co:Mn:Al=58.4:26.4:3.3:1.3:3.0:3.8:0.0.
 6. TheV-Ti-Zr-Ni-Cr electrochemical hydrogen storage alloy of claim 5 havingincreased cycle life with respect to the cycle life of V_(4-y) Ni_(y)Ti_(2-x) Zr_(x) Cr_(z)
 7. The V-Ti-Zr-Ni-Cr electrochemical hydrogenstorage alloy of claim 5 having increased mid-point voltage with respectto the midpoint voltage of V_(4-y) Ni_(y) Ti_(2-x) Zr_(x) Cr_(z)
 8. TheV-Ti-Zr-Ni-Cr electrochemical hydrogen storage alloy of claim 5 havingincreased low temperature capacity with respect to the low temperaturecapacity of V_(4-y) Ni_(y) Ti_(2-x) Zr_(x) Cr_(z)
 9. The V-Ti-Zr-Ni-Crelectrochemical hydrogen storage alloy of claim 5 having increased lowtemperature voltage with respect to the low temperature voltage ofV_(4-y) Ni_(y) Ti_(2-x) Zr_(x) Cr_(z)
 10. The V-Ti-Zr-Ni-Crelectrochemical hydrogen storage alloy of claim 5 having reducedinternal resistance with respect to the internal resistance of V_(4-y)Ni_(y) Ti_(2-x) Zr_(x) Cr_(z)
 11. The V-Ti-Zr-Ni-Cr electrochemicalhydrogen storage alloy of claim 14 having increased cycle life withrespect to the cycle life of V_(4-y) Ni_(y) Ti_(2-x) Zr_(x) Cr_(z) 12.The V-Ti-Zr-Ni-Cr electrochemical hydrogen storage alloy of claim 1having increased mid-point voltage with respect to the midpoint voltageof V_(4-y) Ni_(y) Ti_(2-x) Zr_(x) Cr_(z)
 13. The V-Ti-Zr-Ni-Crelectrochemical hydrogen storage alloy of claim 1 having increased lowtemperature capacity with respect to the low temperature capacity ofV_(4-y) Ni_(y) Ti_(2-x) Zr_(x) Cr_(z)
 14. The V-Ti-Zr-Ni-Crelectrochemical hydrogen storage alloy of claim 1 having increased lowtemperature voltage with respect to the low temperature voltage ofV_(4-y) Ni_(y) Ti_(2-x) Zr_(x) Cr_(z)
 15. The V-Ti-Zr-Ni-Crelectrochemical hydrogen storage alloy of claim 1 having reducedinternal resistance with respect to the internal resistance of V_(4-y)Ni_(y) Ti_(2-x) Zr_(x) Cr_(z)
 16. A reversible, multicomponentV-Ti-Zr-Ni-Cr- electrochemical hydrogen storage alloy having at leastone modifier therein which increases the low temperature voltage of thealloy measured in a sealed, rechargeable, electrochemical cell, saidalloy having the composition:

    (V.sub.y'-y Ni.sub.y Ti.sub.x'-x Zr.sub.x Cr.sub.z).sub.a Co.sub.b Mn.sub.c Al.sub.d

wherein x' is between 1.8 and 2.2, x is between 0 and 1.5, y' is between3.6 and 4.4, y is between 0.6 and 3.5, z is between 0.00 and 1.44, adesignates that the V-Ni-Ti-Zr-Cr component (V_(4-y) Ni_(y) Ti_(2-x)Zr_(x) Cr_(z)), as a group, is at least 70 atomic percent of the alloy,the sum of c+d is a positive number and the sum of b+c+d is an effectiveamount of modifiers up to 30 atomic percent of the alloys.
 17. TheV-Ti-Zr-Ni-Cr electrochemical hydrogen storage alloy of claim 16 whereinthe Mn and Al partially replace V-Ti-Zr-Ni-Cr as a group.
 18. TheV-Ti-Zr-Ni-Cr electrochemical hydrogen storage alloy of claim 17 havinga composition within the homogeneity range of

    V.sub.20.6 Ti.sub.15 Ni.sub.30 Cr.sub.6.6 Mn.sub.3.6 Al.sub.2.7.


19. A reversible, multicomponent V-Ti-Zr-Ni-Cr electrochemical hydrogenstorage alloy having at least one modifier therein which increases thelow temperature hydrogen storage capacity of the alloy measured in asealed, rechargeable, electrochemical cell, said alloy having thecomposition:

    (V.sub.y'-y Ni.sub.y Ti.sub.x'-x Zr.sub.x Cr.sub.z).sub.a Co.sub.b Mn.sub.c Al.sub.d

where x' is between 1.8 and 2.2, x is between 0 and 1.5, y' is between3.6 and 4.4, y is between 0.6 and 3.6, z is between 0.00 and 1.44, adesignates that the V-Ni-Ti-Zr-Cr component, (V_(4-y) Ni_(y) Ti_(2-x)Zr_(x) Cr_(z)), as a group, is at least 70 atomic percent of the alloy,and the sum of c+d is a positive number and the sum of b+c+d is aneffective amount of modifiers up to 30 atomic percent of the alloys. 20.The V-Ti-Zr-Ni-Cr electrochemical hydrogen storage alloy of claim 19wherein the Co modifier partially replaces one or more of V and Ni, andpartially replaces V-Ti-Zr-Ni-Cr.
 21. The V-Ti-Zr-Ni-Cr electrochemicalhydrogen storage alloy of claim 19 having a composition within thehomogeneity range of

    V.sub.20.6 Ti.sub.15 Zr.sub.15 Ni.sub.30 Cr.sub.6.6 Mn.sub.3.6 Al.sub.2.7.


22. A reversible, multicomponent V-Ti-Zr-Ni-Cr electrochemical hydrogenstorage alloy having at least one modifier therein which increases thespecific capacity of the alloy measured in a sealed, rechargeable,electrochemical cell, said alloy having the composition:

    (V.sub.y'-y Ni.sub.y Ti.sub.x'-x Zr.sub.x Cr.sub.z).sub.a Co.sub.b Mn.sub.c Al.sub.d

where x' is between 1.8 and 2.2, x is between 0 and 1.5, y' is between3.6 and 4.4, y is between 0.6 and 3.6, z is between 0.00 and 1.44, adesignates that the V-Ni-Ti-Zr-Cr component, (V_(4-y) Ni_(y) Ti_(2-x)Zr_(x) Cr_(z)), as a group, is at least 70 atomic percent of the alloy,the sum of c+d is a positive number and the sum of b+c+d is an effectiveamount of modifiers up to 30 atoms percent of the alloys.
 23. TheV-Ti-Zr-Ni-Cr electrochemical hydrogen storage alloy of claim 22 havinga composition within the homogeneity range of

    V.sub.20.6 Ti.sub.15 Zr.sub.15 Ni.sub.30 Cr.sub.6.6 Mn.sub.3.6 Al.sub.2.7.


24. A reversible, multicomponent V-Ti-Zr-Ni-Cr electrochemical hydrogenstorage alloy having at least one modifier there in which increases themidpoint voltage on discharge of the alloy measured in a sealed,rechargeable, electrochemical cell, said alloy having the composition:

    (V.sub.y'-y Ni.sub.y Ti.sub.x'-x Zr.sub.x Cr.sub.z).sub.a Co.sub.b Mn.sub.c Al.sub.d

where x' is between 1.8 and 2.2, x is between 0 and 1.5, y' is between3.6 and 4.4, y is between 0.6 and 3.5, z is between 0.00 and 1.44, adesignates that the V-Ni-Ti-Zr-Cr component, (V_(y'-y) Ni_(y) Ti_(2-x)Zr_(x) Cr_(z)), as a group, is at least 70 atomic percent of the alloy,the sum of c+d is a positive number and the sum of b+c+d is an effectiveamount of modifiers up to 30 atomic percent of the alloys.
 25. TheV-Ti-Zr-Ni-Cr electrochemical hydrogen storage alloy of claim 24 havinga composition with the homogeneity range of

    V.sub.20.6 Ti.sub.15 Zr.sub.15 Ni.sub.30 Cr.sub.6.6 Mn.sub.3.6 Al.sub.2.7.


26. A reversible, multicomponent V-Ti-Zr-Ni-Cr electrochemical hydrogenstorage alloy having at least one modifier therein which increases thecycle lift of the alloy measured in a sealed, rechargeable,electrochemical cell, said alloy having the composition:

    (V.sub.y'-y Ni.sub.y Ti.sub.x'-x Zr.sub.x Cr.sub.z).sub.a Co.sub.b Mn.sub.c Al.sub.d

where x' is between 1.8 and 2.2, x is between 0 and 1.5, y' is between3.6 and 4.4, y is between 0.6 and 3.5, z is between 0.00 and 1.44, adesignates that the V-Ni-Ti-Zr-Cr component, (V_(4-y) Ni_(y) Ti_(2-x)Zr_(x) Cr_(z)), as a group, is at least 70 atomic percent of the alloy,the sum of c+d is a positive number and the sum of b+c+d is an effectiveamount of modifiers up to 30 atomic percent of the alloys.
 27. TheV-Ti-Zr-Ni-Cr electrochemical hydrogen storage alloy of claim 26 havinga composition within the homogeneity range of

    V.sub.20.6 Ti.sub.15 Zr.sub.15 Ni.sub.30 Cr.sub.6.6 Mn.sub.3.6 Al.sub.2.7.


28. A modified V-Ti-Zr-Ni-Cr electrochemical hydrogen storage alloyhaving a composition within the homogeneity range of

    V.sub.20.6 Ti.sub.15 Zr.sub.15 Ni.sub.30 Cr.sub.6.6 Co.sub.6.6 Mn.sub.3.6 Al.sub.2.7.


29. The modified V-Ti-Zr-Ni-Cr electrochemical hydrogen storage alloy ofclaim 28 wherein is a multiphase alloy and individual phases of thealloy have compositions within the homogeneity ranges of:(i)Zr:Ti:Ni:V:Co:Mn:Al=92.3:1.3:5.4:0.7:0.3; (ii)V:Ti:Zr:Ni:Cr:Co:Mn:Al=19.6:14.8:17.0:28.7:6.8:8.0:4.0:1.2; (iii)Ti:Zr:Ni:V:Co:Mn:Al=32.3:42.5:7.2:6.2:1.0:6.3:1.5:3.2; and (iv)V:Cr:Ti:Zr:Ni:Co:Mn:Al=58.4:26.4:3.3:1.3:3.0:3.8:0.0.
 30. TheV-Ti-Zr-Ni-Cr electrochemical hydrogen storage alloy of claim 28 havingincreased cycle life with respect to the cycle life of V_(4-y) Ni_(y)Ti_(2-x) Zr_(x) Cr_(z)
 31. The V-Ti-Zr-Ni-Cr electrochemical hydrogenstorage alloy of claim 28 having increased mid-point voltage withrespect to the midpoint voltage of V_(4-y) Ni_(y) Ti_(2-x) Zr_(x) Cr_(z)32. The V-Ti-Zr-Ni-Cr electrochemical hydrogen storage alloy of claim 28having increased low temperature capacity with respect to the lowtemperature capacity of V_(4-y) Ni_(y) Ti_(2-x) Zr_(x) Cr_(z)
 33. TheV-Ti-Zr-Ni-Cr electrochemical hydrogen storage alloy of claim 28 havingincreased low temperature voltage with respect to the low temperaturevoltage of V_(4-y) Ni_(y) Ti_(2-x) Zr_(x) Cr_(z)
 34. The V-Ti-Zr-Ni-Crelectrochemical hydrogen storage alloy of claim 28 having reducedinternal resistance with respect to the internal resistance of V_(4-y)Ni_(y) Ti_(2-x) Zr_(x) Cr_(z)
 35. A V-Ti-Zr-Ni-Cr electrochemicalhydrogen storage alloy as in claim 1, including a modifier "M" selectedfrom the group consisting essentially of Mo, Cu, W, Fe and combinationsthereof wherein the alloy has the composition:

    (V.sub.y'-y Ni.sub.y Ti.sub.x'-x Zr.sub.x Cr.sub.z).sub.a Co.sub.b Mn.sub.c Al.sub.d M.sub.3

and e is from 0 to 20 atomic percent of the alloy and the sum of b+c+d+eis up to 30 atomic percent of the alloy.
 36. A V-Ti-Zr-Ni-Crelectrochemical hydrogen storage alloy as in claim 16, including amodifier "M" selected from the group consisting essentially of Mo, Cu,W, Fe and combinations thereof wherein the alloy has the composition:

    (V.sub.y'-y Ni.sub.y Ti.sub.x'-x Zr.sub.x Cr.sub.z).sub.a Co.sub.b Mn.sub.c Al.sub.d M.sub.e

and each of b, c, d and e is from 0 to 20 atomic percent of the alloyand the sum of b+c+d+e is up to 30 atomic percent of the alloy.
 37. AV-Ti-Zr-Ni-Cr electrochemical hydrogen storage alloy as in claim 19,including a modifier "M" selected from the group consisting essentiallyof Mo, Cu, W, Fe and combinations thereof wherein the alloy has thecomposition:

    (V.sub.y'-y Ni.sub.y Ti.sub.x'-x Zr.sub.x Cr.sub.z).sub.a Co.sub.b Mn.sub.c Al.sub.d M.sub.e

and each of b, c, d and 3 is from 0 t 20 atomic percent of the alloy andthe sum of b+c+d+e is up to 30 atomic percent of the alloy.
 38. AV-Ti-Zr-Ni-Cr electrochemical hydrogen storage alloy as in claim 22,including a modifier "M" selected from the group consisting essentiallyof Mo, Cu, W, Fe and combinations thereof wherein the alloy has thecomposition:

    (V.sub.y'-y Ni.sub.y Ti.sub.x'-x Zr.sub.x Cr.sub.z).sub.a Co.sub.b Mn.sub.c Al.sub.d M.sub.e

and each of b, c, d and e is from 0 to 20 atomic percent of the alloyand the sum of b+c+d+e is up to 30 atomic percent of the alloy.
 39. AV-Ti-Zr-Ni-Cr electrochemical hydrogen storage alloy as in claim 24including a modifier "M" selected from the group consisting essentiallyof Mo, Cu, W, Fe and combinations thereof wherein the alloy has thecomposition:

    (V.sub.y'-y Ni.sub.y Ti.sub.x'-x Zr.sub.x Cr.sub.z).sub.a Co.sub.b Mn.sub.c Al.sub.d M.sub.e

and each of b, c, d and e is from 0 to 20 atomic percent of the alloyand the sum of b+c+d+e is up to 30 atomic percent of the alloy.
 40. AV-Ti-Zr-Ni-Cr electrochemical hydrogen storage alloy as in claim 26,including a modifier "M" selected from the group consisting essentiallyof Mo, Cu, W, Fe and combinations thereof wherein the alloy has thecomposition:

    (V.sub.y'-y Ni.sub.y Ti.sub.x'-x Zr.sub.x Cr.sub.z).sub.a Co.sub.b Mn.sub.c Al.sub.d M.sub.e

and each of b, c, d and 3 is from 0 to 20 atomic percent of the alloyand the sum of b+c+d+e is up to 30 atomic percent of the alloy.
 41. Amodified V-Ti-Zr-Ni-Cr electrochemical hydrogen storage alloy having acomposition within the homogeneity range of:

    V.sub.22 Ti.sub.16 Zr.sub.16 Ni.sub.27.8 Cr.sub.7 Co.sub.5.9 Mn.sub.3.1 Al.sub.2.2.